California’s battleground races for the House of Representatives are pivotal again this election year, and Tuesday’s primaries could provide more clues about which party will win control of Congress in November.

In one Central Valley district, Republicans could even lock up a seat in Tuesday’s election because of a Democratic intraparty fight and California’s open primary rules.

California, the nation’s most populous state, is expected to have 10 of the 72 most competitive House races in the country, according to the nonpartisan Cook Political Report. Republicans currently have a narrow 219-213 majority in the House.

In the past few election cycles, races in several of those California districts have been decided by a couple thousand or even a few hundred votes. Some districts have changed hands multiple times since the so-called blue wave of 2018, when Democrats won seats in the state that were once considered solidly Republican.

California is now considered a perennial battleground, where both parties must spend heavily every election cycle.

“It’s because of the volatility of the party balance, with these House races going back and forth,” said Raphael Sonenshein, the executive director of the Haynes Foundation, a political science research nonprofit in the Los Angeles region.

In several cases, the same candidates from 2022 are facing off again. “It used to be, if you lost, they didn’t want to hear from you,” Mr. Sonenshein said. “Now, you have a certain amount of name recognition.”

In close contests, the outcome may not be known for days or weeks because of the state’s long counting process and heavy reliance on mail ballots. It may not be clear for weeks who will be on the ballot in the fall. Here are the key California House races to watch:

22nd Congressional District

Republicans could secure a battleground seat on Tuesday — months before the November general election — in a district where Democrats have a voter registration advantage.

Representative David Valadao, a Republican, is vulnerable in his Central Valley district, as he has been every time he has run for re-election. But even though the district has more registered Democrats than Republicans, Central Valley Democrats are more conservative than those on the coast, and the 22 percent of voters who have declared no party preference could swing either way. A Democratic intraparty fight may split the vote enough to allow Mr. Valadao and another Republican, Chris Mathys, to take the top two spots.

Under California’s open primary system, only the top two vote-getters advance to the general election, regardless of party. That means if the two Democrats, Rudy Salas and Melissa Hurtado, finish in third and fourth, Mr. Valadao and Mr. Mathys will advance to the general election and lock up the seat for Republicans.

Democrats are concerned about the potential danger of not coalescing behind one candidate in March — enough that Gov. Gavin Newsom and Dolores Huerta, the 93-year-old farm labor leader, recently visited the district and urged voters to support Mr. Salas, a former state assemblyman who lost to Mr. Valadao in 2022.

But Ms. Hurtado, a state senator, believes she has a better shot at taking the seat in November, and her current district overlaps with 95 percent of the House district. She has to run not only against Mr. Salas and the two Republicans, but also against the wishes of House Democratic leadership, which has spent precious dollars backing Mr. Salas in the primary.

Mr. Valadao is perhaps the most unloved congressman in California, targeted by Democrats every year, yet under fire from conservatives for his moderate positioning in his swing district. In 2021, he was one of only 10 Republicans who voted to impeach former President Donald J. Trump for inciting the Capitol riot on Jan. 6, 2021. Mr. Valadao’s impeachment vote may appeal to the 42 percent of district voters who are registered Democrats, but it makes him vulnerable to Mr. Mathys, a more conservative Republican, in the primary.

If one Democrat survives, another expensive battle is likely to take place in November.

13th Congressional District

The Central Valley is ripe for swing districts, but unlike the 22nd Congressional District, this race does not feature a primary fracas.

Two candidates are already heading for a rematch of their tight 2022 contest: Representative John Duarte, the Republican incumbent, and Adam C. Gray, a former Democratic state lawmaker.

The two men have described themselves as moderates. In 2022, both candidates prioritized water access for the agricultural region during their campaigns. Mr. Duarte, a farmer, won by less than 600 votes.

47th Congressional District

When Katie Porter, a progressive Democrat, was elected to represent her Orange County district in the House in 2018, she took over a seat that had been comfortably occupied by Republicans for years. Her ascendance heralded a change in a longtime Republican stronghold where increasingly diverse suburban voters had pulled the electorate to the left.

But the seat became open when Ms. Porter decided to run for Senate, forcing Democrats to fight for the seat without an incumbent.

Scott Baugh, who lost to Ms. Porter by about three percentage points in 2022, is making his second attempt to reclaim the seat for Republicans. He is a local Republican Party official who served in the state legislature more than two decades ago and owns a law firm.

Among the four Democrats on the ballot, two have emerged as serious contenders to face Mr. Baugh in November. Dave Min, a state senator who has taught law at the University of California, Irvine, has received key endorsements from the California Democratic Party, Ms. Porter and the California Labor Federation. Despite his establishment support, his path became more complicated after he pleaded no contest to driving under the influence last year.

Joanna Weiss, a Democratic community organizer who has also worked as a law professor, has made abortion rights a focus of her campaign, which has won the backing of Emily’s List and the California Young Democrats.

40th Congressional District

Representative Young Kim, a Republican who is serving her second term in Congress, is seeking to fend off challenges from two Democrats: Joe Kerr, a retired fire captain and former union leader; and Allyson Muñiz Damikolas, a Tustin Unified School District board member.

The Cook Political Report has called Kim’s seat “likely Republican.” In 2022, Ms. Kim, one of the first Korean American women in Congress, won a second term by 14 points. But Democrats still see the district, which covers portions of Orange, Riverside and San Bernardino Counties, as a potential flip. President Biden narrowly carried the district by two points in 2020.

Ms. Muñiz Damikolas has been endorsed by the California Teachers Association, Emilys List and the National Organization for Women. Mr. Kerr is backed by the California Labor Federation and California School Employees Association.

41st Congressional District

Tuesday’s primary is expected to set up a rematch in November between Representative Ken Calvert, the longtime Republican incumbent, and Will Rollins, an openly gay Democrat and former federal prosecutor who lost to Mr. Calvert by less than five percentage points in 2022.

While Mr. Calvert has represented parts of the Inland Empire for three decades, the district became less conservative after a 2021 redistricting process that added Palm Springs, a liberal bastion that some residents call the gayest city in America.

Democrats have once again thrown their weight behind Mr. Rollins, and both parties are already spending heavily on the race, which the Cook Political Report has called a tossup.

The candidates have already gone into attack mode. In ads, Mr. Calvert has sought to depict Mr. Rollins as “the worst kind” of prosecutor who is “soft on crime.” Mr. Rollins has released his own ad that refers to a 1993 incident in which Mr. Calvert acknowledged being with a prostitute in his car. The police confronted Mr. Calvert but did not charge him in the incident.

Four Democratic challengers are hoping to unseat Representative Michelle Steel, the Republican incumbent, in the district that covers inland Orange County and a small part of Los Angeles. Ms. Steel, one of the first Korean American women in Congress, is serving her second term in Congress, where she has mostly voted along party lines.

The district, which Mr. Biden won in 2020, is a showcase for Asian American political power. Asian Americans make up more than a third of the electorate in the district, and almost half of them are Vietnamese Americans, many of whom still have strong memories of fleeing a communist government and have a tendency to lean right politically.

Ms. Steel’s Democratic opponents include Kim Nguyen-Penaloza, a Garden Grove City Council member who has been endorsed by the California Democratic Party; and Derek Tran, a veteran and consumer rights attorney who has been endorsed by several prominent California politicians, including Representative Judy Chu. Both Ms. Nguyen-Penaloza and Mr. Tran are of Vietnamese heritage.

27th Congressional District

In a key battleground north of Los Angeles, Representative Mike Garcia, the Republican incumbent and a former military pilot, is facing challenges from two Democrats — George Whitesides, the former chief executive of Virgin Galactic, and Steve Hill, a former U.S. Marine and a self-professed Satanist.

Mr. Garcia first won the seat by defeating Christy Smith, a former Democratic state lawmaker, in a special election in May 2020. Mr. Garcia went on to defeat Ms. Smith two more times, even after a redistricting process that was expected to favor the Democrats.

But Democrats still see an opportunity this fall. In 2020, Mr. Biden beat Mr. Trump in the district by more than 12 percentage points. Hoping to shake up the dynamics, Democrats recruited Mr. Whitesides, a political newcomer who has drawn on ample fund-raising and his own personal wealth to support his campaign.

20th Congressional District

This is a safe Republican district, but it is worth mentioning as the seat vacated by Kevin McCarthy, the former speaker of the House, at the end of 2023 after he was ousted from the top leadership position by fellow Republicans.

The two leading Republican candidates are Vince Fong, a state assemblyman, and Mike Boudreaux, the Tulare County sheriff. The two grew up in the Central Valley region but have had different paths — Mr. Fong in politics and Mr. Boudreaux in law enforcement.

Mr. Fong has longstanding ties to the Republican establishment in the region and worked for Mr. McCarthy, who has backed him. Mr. Boudreaux has run as a law-and-order conservative to the right of Mr. Fong.

But Mr. Fong received the biggest endorsement prize when Mr. Trump called on voters last month to unite around him in the race. He has also been endorsed by Speaker Mike Johnson and most of the Republican delegation from California.

Because the House seat is vacant, several candidates, including Mr. Boudreaux and Mr. Fong, are running in Tuesday’s primary for a full term in the next Congress, as well as a special election primary on March 19 to fill the seat on an interim basis.

Mr. Fong faces an additional wrinkle: Because he filed to run for Congress after filing for re-election in the State Assembly, there was a legal fight about whether he could remain on the ballot for both seats. A Sacramento judge ruled in Mr. Fong’s favor, but Shirley Weber, the secretary of state, has appealed that decision.