When he’s not at work as the powerful, even feared, staff di rector of the influential Senate Finance Committee, he’s roaring through Washington on his Harley Davidson. On weekends he heads home to Manhattan to be with his movie-star wife and infant daughter.

He is pals with entertainment industry creatures of every stripe, from moguls to writers. He has appeared on “Saturday Night Live,” and other TV producers lust after him. Cristophe (who else?) has cut his hair. And he savors his standing as a Capitol Hill outsider, shaking things up, picking up some enemies but no regrets–a short-timer dropping by in devoted service to Sen. Daniel Patrick Moynihan (D-N.Y.)

O’Donnell’s days as staff director for the Finance Committee are long and hectic. It’s not uncommon for him to work 18-hour days–assisting Moynihan on the Senate floor and meeting with other senators and their staffs. He spends hours fielding telephone calls from everyone from White House advisers to the media to consumer advocate Ralph Nader. Back-to-back meetings getting an earful from lobbyists, barking out orders to staffers and lining up votes are all part of a day’s work.

Loved and loathed, respected and feared, he shatters the stereotype of your typical Senate staffer–especially one who has the task of ushering through committee such weighty legislation as health care and welfare reform, the budget and NAFTA.

Said White House adviser George Stephanopoulos, who has worked closely with O’Donnell on major issues: “How many staff directors drive motorcycles and commute to New York to write screenplays?”

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On Valentine’s Day this year, O’Donnell and Kathryn Harrold stopped in Las Vegas on their way to Los Angeles, where they have a home, and got married in a quickie ceremony.

She was about five months pregnant, and Capitol Hill’s irony mavens noted with relish that O’Donnell’s boss has long made an issue of the problem of children born out of wedlock. Although some joked that an embarrassed Moynihan had pressured his committee staff director to get married, O’Donnell denied that it was ever an issue. Moynihan agreed: “I wouldn’t dream of it. They were an old married couple when I met them.”

To those who admire O’Donnell–whose sarcasm and wit endeared him to his colleagues at the Harvard Lampoon–he is a flash of brilliance and creativity, a diamond among Washington’s ranks of drab bureaucrats.

“He’s the luckiest man I know because he’s married to Kathryn Harrold, he’s maybe the smartest man and he sure as hell is the toughest,” Moynihan said.

“When you meet someone like him in Washington, it’s refreshing,” said Sen. Barbara Boxer (D-Calif.) “He’s a pragmatist. He doesn’t have much patience for wasted words. God, that’s a relief.”

Jack Valenti, president of the Motion Picture Assn. of America, called O’Donnell “a Renaissance man. He’s a unique . . . and dashing fellow. One thing he is not, is dull.”

But to those who disdain O’Donnell, a 42-year-old native of Boston, he is imperious, egotistical, foul-mouthed and Machiavellian. “He has an ego as big as a senator,” said someone from the White House who has dealt with O’Donnell. This person, like all of O’Donnell’s critics, insisted on anonymity.

O’Donnell said he couldn’t care less about what people think of him. “I don’t for one second spend any time thinking about carefully ingratiating myself with someone for the future.”

He said he came to Washington to work for Moynihan, chairman of the Finance Committee, because of his admiration and respect for the New York Democrat. When he finally gives it up, O’Donnell said he’ll have no desire to stick around. “There is no other thing in Washington I can imagine interesting me. So, I’ll leave with whatever enemies I pick up. . . . And I will ask Washington for no favors when I’m gone.”

“When they say he’s arrogant, I suppose they are referring to his capacity for telling people to go to hell,” said O’Donnell’s father, Lawrence Sr., a 73-year-old Boston lawyer.

“I like pointing my finger in the face of the king, as they say,” he added. “He’s like that, too. He’s not on a hero-worship kick. I would be disappointed if people weren’t taking shots at him. It means he’s shaking things up.”

Since coming to Washington in 1992, O’Donnell has become a frequent guest on the PBS talk show “Charlie Rose.” True to his rogue image, he recently appeared on the program unshaven, wearing a denim shirt, looking as if he’d just roared in on his chopper.

Last year, he turned down an offer by Fox to anchor a news program in Los Angeles. “I was fascinated by the offer. . . . I can’t make a million dollars in the Senate,” he said with a laugh. “I was interested but it came a year too early.”

Now, John Bowman, executive producer of “Murphy Brown,” wants O’Donnell, Moynihan and Sen. Bob Dole (R-Kan.) to appear as guests on the show, although none has yet agreed to do so.

“I would love to have (O’Donnell) on. He’s so cool . . . very funny and incredibly bright, creative . . . and independent,” Bowman said of his friend from their days together at the Harvard Lampoon.

Bowman recalled that O’Donnell was on the business staff of the famed college humor magazine. “I don’t think he ever sold a single ad. But . . . he was so cool they wanted him on the staff whether he did anything or not.”

Even back in college, O’Donnell “never made any attempt to pretend to like anybody he didn’t,” said Bowman, a former “Saturday Night Live” writer. “He was always straightforward. He had a very good sense of himself.”

Lisa Henson, president of Columbia Pictures, described O’Donnell as a kind of “accidental genius.” Henson, who was the first woman editor of the Lampoon, also met O’Donnell at Harvard and the two have been friends since. “He’s sophisticated . . . original and he’s unpredictable,” she said. “He’s so good on his television appearances. I could listen to him talk for hours.”

During the 1992 Democratic convention, he teamed with comedian Al Franken to provide humorous commentary for the Comedy Central cable network, poking fun at, among others, Bill Clinton.

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O’Donnell grew up in the Dorchester area of Boston, the youngest of five children.

“I ended up going to Harvard College, which was about as likely in my neighborhood as going to the moon,” O’Donnell said. Nevertheless, he remained true to the group he grew up with: “I was very much a street guy.”

But even though it was the psychedelic era, O’Donnell–unlike many of his peers–refused to drink, smoke or use drugs, he said.

He admitted making eccentric choices back in high school, college and beyond, though. “I was an extreme leftist-anarchist. Now, I guess I’m a European socialist who’s locked into American citizenship, without complaint.”

His father said O’Donnell was the kind of kid who would leave the comforts of the family’s summer home at Cape Cod and go into the city to “clean out dirty buildings for a civic association . . . to create housing for people.”

After graduating from Harvard with a degree in economics, O’Donnell said he was “an itinerant writer,” working on everything from TV pilots to Op-Ed pieces, and hung out in New York clubs.

In 1977, while working as a parking attendant in the Combat Zone section of Boston, his father came to tell him about a police brutality case he was working on.

“ ‘It’s the best case I’ve ever had and I think you could write about it,’ he told me,” the younger O’Donnell said. “That week, I went up to his office, sat down and read through 30 police reports on the case and was just permanently mesmerized by this story.”

Working as a researcher and investigator for his father, they sued the Boston Police Department on behalf of an African American mother whose husband had been shot and killed two years earlier by two police officers.

The five-year court fight led to the downfall of a police commissioner and prompted a book by the younger O’Donnell, “Deadly Force” (William Morrow, 1983), which was later turned into a television movie.

During this time, O’Donnell said, he was attacked, beaten and arrested in the parking lot where he worked by officers from the same unit involved in the brutality case. He later sued the police for violation of his civil rights. He won damages in federal court, his father said.

By the time Harrold, who has appeared as a regular on “I’ll Fly Away” and “The Larry Sanders Show,” met him about six years ago, O’Donnell had gone through most of the money he had earned from the book and movie. (He also had shared some of the proceeds with the widow, his father said.)

“Lawrence was doing nothing. He was absolutely broke,” Harrold recalled. “He had been really poor while he was writing the book, and he hadn’t been making a cent.”

So when money finally did start coming in, she added, “I think he just lived like a normal human being. He did things like buy clothes. And he got a nice apartment, which he deserved.”

They met at a surprise 30th birthday party for one of O’Donnell’s New York housemates at the time, Maura Moynihan, the Senator’s daughter.

“I think he’d gone through just about everything,” Harrold said. “But I said, ‘here’s this great guy, this really smart, funny, wonderful person.’ And that’s all that mattered to me. So, whatever happens with (Lawrence) is just gravy.”

Through his daughter, Moynihan met O’Donnell and was dazzled by him–”it was a match made in heaven,” Maura Moynihan said–and within months, the Senator had hired the political novice to work on his 1988 reelection campaign. O’Donnell quickly became Moynihan’s senior adviser, then Finance Committee staff director.

Like his friend and mentor, Moynihan, O’Donnell’s political philosophy evolved over the years. He said the difference between his views in the 1970s and now is that “I no longer resent the idea that Bob Dole has a vote, and an important one.”

“There was the slow discovery for me in the early ‘80s that Republicans are people too. . . . That Republicans are perfectly reasonable people . . . and that Republicans can be right about something.”

He’s been described as Moynihan’s alter ego. But “that couldn’t be more absurd,” O’Donnell said. Moynihan has more education, more experience, has written more books and is far more industrious, he argued. “I personally, can’t think of a greater insult to Sen. Moynihan or a greater praise to me.”

Sen. Boxer said O’Donnell is “extremely effective because of his special relationship with Pat Moynihan. That kind of relationship is rare in life. There is a certain kinship there.”

Others are quick to criticize that relationship.

“Lawrence brings out the worst in Moynihan,” said a White House staffer. “He fosters and encourages the testy Moynihan, the easily offended Moynihan, the Moynihan who reads insults when they are not given.”

Said one Administration official: “He’s adopted Moynihan’s intellectual arrogance, but without the intellect.”

Moynihan rejects the suggestion by some that O’Donnell has been given too much clout. “If I had any more power, I would give that to him too. . . . He’s a superbly able man,” he said.

This week, Moynihan–with O’Donnell at his side–led Senate debate on the health care bill offered by Majority Leader George Mitchell (D-Me.). Mitchell’s health care plan incorporates much of the original bill O’Donnell helped forward through the Finance Committee in June. (The House is considering another plan put forward by House Majority Leader Richard Gephardt (D-Mo.) and Senate Republicans are pushing yet another version put together by Minority Leader Dole (R-Kan.)).

There had been talk on Capitol Hill that some senators, staff and even White House officials were furious about actions and remarks by Moynihan and O’Donnell they felt undermined Clinton’s health care plan in the Finance Committee.

White House adviser Stephanopoulos denies that the White House has any ill feelings toward them or thinks that they dropped the ball on health care.

“They did their best,” he said. “It’s tough.”

He also denied that there were any hard feelings over Moynihan’s televised description of part of the President’s health plan as fantasy.

“Just bumps in the road,” Stephanopoulos said.

As far as their work on health care reform, Boxer defended O’Donnell and Moynihan.

“I believe that had Daniel Patrick Moynihan and O’Donnell . . . done everything as the President said, they would not have had a bill at all.

“In the end, the White House may have thought they were obstructionists. But in truth, they were the saviors because they maintained a level of independence.”

Meanwhile, Harrold said she doesn’t believe that her husband will pack up and leave Washington when he’s finished working with Moynihan.

“He’s addicted,” she said. Politics “gets in their blood. And it’s happened to him.”