About 4 in 10 registered Democrats and nonpartisan voters in the survey said they hadn’t made up their minds on a candidate, so the race still has plenty of room to shift between now and the March 2024 primary.

Among those who have decided, however, Reps. Adam B. Schiff of Burbank and Katie Porter of Irvine are nearly tied and hold a strong early lead ahead of two other hopefuls, Reps. Barbara Lee of Oakland, who declared her candidacy this week, and Ro Khanna of Fremont, who has been considering whether to get into the fray.

Schiff has the support of 22%, with 20% backing Porter, 6% for Lee and 4% for Khanna, the poll found.

Under the state’s top-two primary system, voters can choose among candidates of any party, with the two who get the most votes advancing to the November election. In 2016 and 2018, two Democrats faced off in general election Senate races.

Because no prominent Republican has gotten into the 2024 race — or even publicly discussed entering it — this poll questioned only Democrats and nonpartisan voters about the contest.

Despite being well-known in their respective districts, the candidates will need to do a lot of work to boost their prominence, the poll showed. Each of the four hopefuls was viewed favorably by voters, but huge swaths didn’t know enough to have an opinion of them. That was especially true for Khanna and Lee, who both drew blanks from more than 6 in 10 voters.

“I was thinking to myself: These Congress people, who certainly are prominent in Washington, and they’ve been prominent on TV…. Wait until they see our poll, and they’re going to be shocked at how many people don’t have a clue about who they are or what they stand for,” said Mark DiCamillo, director of the IGS poll, who has surveyed California voters for decades.

The poll showed a sharp age divide between supporters of the two leading candidates.

Schiff, 62, a former federal prosecutor who was first elected to Congress in 2000, has the backing of former House Speaker Nancy Pelosi and other leading figures in the party establishment. That may contribute to his strong support from older voters. Respondents 65 and older favor him over Porter, 42% to 17%. He has a smaller, but still significant, lead among voters between the ages of 50 and 64, 27% to 19%.

Porter, 49, a professor at UC Irvine, was elected to Congress in 2018 in a swing Orange County district and rose to prominence through fiery performances at oversight hearings in recent years. She’s popular among voters younger than 40, with about 20% of them saying they support her compared with 8% for Schiff.

Geographically, Porter has a strong advantage over Schiff in Orange County and a 2-1 lead in the Inland Empire.

Schiff leads in the San Francisco Bay Area (23% to 16%), the Central Valley (19% to 13%) and the Central Coast (25% to 16%).

The two are basically tied in Los Angeles County, where about a quarter of the state’s voters reside, and in San Diego County.

Political consultant Doug Herman, who recently helped former Rep. Karen Bass get elected mayor of Los Angeles, said the top priority right now for these candidates is raising money — always a consideration for campaigns in a massive state that is divided among expensive media markets.

Porter and Schiff are both coming off banner fundraising years.

Porter pulled in more than $25 million for her last congressional campaign. But she had to spend heavily to beat back a formidable Republican challenger and now has $7.7 million in the bank. Schiff had more than $20 million on hand as of his last campaign finance report in late November.

Lee faced little competition in her deep-blue Oakland district while spending more than $2 million in her last campaign. She ended the race with less than $55,000 in the bank.

Voters at this point are most interested in the candidates’ values and personalities, as opposed to specific policy positions, Herman noted. That’s likely to be especially true in this race, in which the candidates have very similar voting records.

His lead in the Bay Area and his advantage among older voters gives Schiff an edge, Herman noted. Older voters are the most likely to vote, especially in primaries.

Schiff built up credibility with older Democratic voters with his prominent role leading the first impeachment of former President Trump in 2019 and 2020, Herman said.

“These are the people who watched him defend the country against Trump’s attacks on Ukraine and electioneering,” Herman said of the groups among whom Schiff leads.

“They’re the people you’d want most to have behind you first and last, and he’s already coalesced that at a pretty solid rate.”

When he jumped into the race, Schiff said he wouldn’t take money from corporate political action committees. Porter was quick to note in a campaign email that she had not taken this sort of largesse for some time.

Porter couples her criticism of corporate donations with reminders to voters about her experience working for then-California Atty. Gen. Kamala Harris as the state’s independent monitor of a $25-billion mortgage settlement with banks.

She has become well-practiced in the art of the viral moment — whether it be during a committee hearing or during the speaker election in January, when she was spotted on the House floor reading a book titled “The Subtle Art of Not Giving a F—.”

Those instances in which Porter went viral on social media have endeared her to many progressives. She leads Schiff 31% to 20% among voters who identify as strongly liberal. Schiff leads among moderates, 22% to 10%, but 46% in that group are undecided.

Lee, who entered the race this week, comes with sterling progressive and liberal bona fides. The 76-year-old Oakland native was quick to highlight that she was the lone person in Congress to vote no in 2001 on authorizing the use of military force after the Sept. 11 attacks.

She has also highlighted her background as a young single mother on public assistance and a domestic violence survivor.

Nonetheless, she runs a distant third among strongly liberal voters.

If either Schiff or Porter were to win in November, the state would have two senators from Southern California for the first time in more than half a century. So far, that doesn’t appear to be bothering voters. Just 18% said it was important to have a Bay Area native in the job. Even among that group, Schiff and Porter narrowly edged out Lee. Twenty-four percent of voters said it was important to have a Southern Californian.

Porter led among the 15% of voters who said it was “very important” to elect a woman. A total of 44% of those polled said it was important to elect a woman, compared with 47% who said it was not important. Twelve percent of respondents said it was very important to have a person of color in the post, but among those who expressed that view, Porter, who is white, led Lee, who is a former chair of the Congressional Black Caucus, 20% to 14%.

Respondents almost unanimously said they wanted a candidate who was willing to negotiate and work collaboratively with others to get things done. But 8 in 10 also said it was important to have someone who would “fight uncompromisingly for what they believe in.” Neither of those preferences seemed to have much effect on voters’ choice of candidates.

About three-quarters of respondents said it was important to have a candidate who was progressive, while only 20% said that was not important.

As for Feinstein, who announced this month that she would not run again, a resounding majority, 64%, said it was a good idea for the 89-year-old to step aside, while 28% had no opinion. Just 8% said it was a bad idea. Thirty-seven percent of respondents had a favorable view of the senator, while 43% had an unfavorable one.

Bill Carrick, a longtime political advisor to the former San Francisco mayor, said he believes Feinstein’s image will grow more favorable as her retirement nears and people spend more time discussing her legacy. In recent years she’s been criticized for the way she handled hearings to confirm Supreme Court Justice Brett M. Kavanaugh, and colleagues and party activists have questioned her age and mental fitness.

“Her numbers are going to get better,” Carrick said.

“People are going to say: ‘Oh, I forgot that she had an assault weapons ban. Oh, I didn’t know she was original sponsor of the same-sex marriage legislation. Oh, she did all that environmental stuff.’”

Pelosi’s early endorsement of Schiff was part of the reason he is performing so strongly in the Bay Area, Carrick said. Similarly, he thought Feinstein’s blessing could help — particularly in San Francisco and its neighboring counties where she remains relatively popular compared with the rest of the state.

On the day she announced she wouldn’t run again, Feinstein also told reporters she would endorse a successor but that choice would be made in “a couple months.”

“I’ll talk about that later. I don’t have anybody in mind right now,” she said.

The Berkeley IGS poll was conducted Feb. 14-20 among 7,512 California registered voters, of whom 5,681 were registered Democrats or “No Party Preference.” The sample was weighted to match census and voter registration benchmarks. Because of weighting, precise estimates of the margin of error are difficult, but the results are estimated to have a margin of error of 2.5 percentage points in either direction for the sample of Democratic and non-party voters.