California Democratic Reps. Howard Berman and Brad Sherman have worked together in Congress for 15 years, but the next year could find them spending millions of dollars telling voters why only one of them should return to Washington.

Their western San Fernando Valley matchup is expected to be one of the most expensive House races ever and has already split the delegation, with 23 of California’s 32 other Democrats endorsing Berman and two backing Sherman.

Rep. Henry Waxman, who represents a neighboring district and is a longtime friend of Berman, believes the endorsement list “says a lot because people ordinarily don’t want to get in the middle of a fight.” In this case they feel so strongly that if they have to choose, they want Berman, Waxman said.

Rep. Jim Costa, who also goes way back with Berman, said he wishes the two Members could avoid the race altogether. Berman allies have urged Sherman to run in the open Ventura County district to the west.

“I think it’s silly for [Berman] and Brad to be running against each other,” Costa said. “Brad’s a decent guy, but there’s that other seat that he could run for. I don’t know why he’s insisting we spend all this money in one race. It makes absolutely no sense politically.”

Berman is raising money at a feverish pace, tapping his connections in the entertainment industry to help bring in $819,000 in the third quarter. He said in an interview that he expects to turn in an “impressive fourth quarter” as well.

Looking ahead, Berman guessed he and Sherman could spend $10 million combined. But he outlined his most important goal: “I will raise enough to do what I need to do to win.”

Sherman has saved up money after a decade of noncompetitive races, the result of lines drawn in 2001 by Berman’s brother, Democratic consultant Michael Berman. With $3.7 million in the bank, Sherman is continuing to emphasize his tireless public appearances in the reshaped district, which, after the state’s newly installed independent redistricting process, includes more than half of his current district and both Members’ homes.

Thanks to the state’s new “top two” primary system, the contest for the strongly Democratic 30th district could last past the June primary and into November. But with one Republican already in the race — businessman Mark Reed, who lost to Sherman in 2010 — and a 25 percent GOP voter registration, Democratic consultant Paul Mitchell said there is a real chance only one of the Democrats could make it to the general.

Because of that, Mitchell said to expect a “mountain of spending in the primary,” as neither wants to be the candidate who lost by 2,000 votes with $4 million in the bank. Berman has already sent out one mailer touting his own leadership.

Sherman has held more than 150 town hall meetings since coming to Congress, something his campaign believes will be the difference in the race.

“Both candidates will have plenty of money to communicate. This will not determine the winner,” Sherman adviser Parke Skelton said. “The winner will be the Member who has done the best job of building a base in the San Fernando Valley. That will be Brad.”

In an interview, Sherman said Berman’s role in helping keep incumbents safe for the past 10 years led to the disparity in endorsements. He said his own record and promise of constituent outreach will make the difference with voters.

“They want someone they know they’re going to see in 2013, 2014 and 2015,” Sherman said. “I’m going to be at the concerts in Warner Center Park standing by my constituent service booth in 2028.”

Skelton also downplayed the importance of Berman’s overwhelming lead in Congressional endorsements. Far more important, he argued, is Sherman’s support from local leaders, unions, Democratic activists and volunteers, and the Democratic Party of the San Fernando Valley.

But Berman and his allies say his overwhelming support from the delegation — from Rep. Mike Thompson’s district near the Oregon border to Rep. Bob Filner on the border with Mexico — should be a sign to voters in the valley that Berman’s colleagues believe he is the more effective Member of Congress.

“There is a larger story in the numbers, 23 to two,” Berman said. “That’s that the people that work with us every day on legislative issues and all kinds of things for California have decided they’re willing to publicly associate with one of us — with me.”

One of the few remaining neutral California Democrats is Rep. Janice Hahn, the newest Member of the delegation and one dealing with a Member-vs.-Member race of her own against fellow Democratic Rep. Laura Richardson in south Los Angeles. Hahn said she’s been focusing on her own race so far but may eventually weigh in on the Sherman-Berman bout.

Los Angeles-based Democratic consultant Roy Behr doesn’t see much of an effect from the endorsements on voting in a race between two longtime incumbents. It could make a difference with donors, he said, “but neither of these guys are short on money.”

“Given the candidates’ similarities in voting records, experience, appearance and even names, I think the race will be won by whichever one does a better job of emerging from the blur of similarity,” Behr said.

Mitchell cautioned that Berman could be setting himself up for an attack line from Sherman by hyping his influence and insider status in Congress, especially if that’s not the message voters are listening for this year.