Democrats think new rules in California could make Rep. Nancy Pelosi speaker of the House again. (J. Scott Applewhite/AP)

Primary voters in California on Tuesday began to remake the face of Congress as a redrawn electoral map and new balloting rules promised a significant overhaul of the state’s delegation, which accounts for about 12 percent of the House of Representatives.

Even before Tuesday’s competitive and expensive primary contests, the changes drove eight veterans of the House into retirement and rattled what had been one of the most stable rosters of lawmakers sent to Washington by any state.

Despite the tumult, both parties see an upside.

Democrats think this could make Rep. Nancy Pelosi speaker of the House again. They contend that they could pick up five seats in California on their way to the 25 they need to retake the majority next year.

Many of the California races remained undecided late Tuesday, but primaries in several other states helped set the stage for the fall elections. In a bitter incumbent-vs.-incumbent race in New Jersey, Democratic Rep. Bill Pascrell Jr. defeated Rep. Steven R. Rothman, a fellow Democrat and onetime friend. With 99 percent of the votes counted, Pascrell led Rothman 61 percent to 38 percent. In a neighboring district in Newark, Democrats nominated Donald M. Payne Jr. to succeed his late father, who was a senior member of the Congressional Black Caucus.

In California, Republicans say the changes, over the long term, have the potential to transform to GOP into a more competitive party, because the new map and the new voting system may force it to nominate centrist candidates who can appeal to the state’s burgeoning population of minority voters.

The battle for supremacy will be fought with money, and both sides expect California to see a flood of dollars from the national parties in Washington.

“It is going to be so expensive,” Sen. Barbara Boxer (D), who is not on the ballot this year, said Tuesday.

One GOP strategist predicted that, going into the general-election campaign, about $30 million will flow into the state from the National Republican Congressional Committee, the Democratic Congressional Campaign Committee and partisan-aligned super PACs for the contests for the 12 seats that are potentially competitive.

That estimate did not include the state’s most expensive race, a battle that has begun to achieve epic dimensions and has acquired the shorthand designation “Berman-Sherman.”

That contest pits 15-term Rep. Howard L. Berman against a colleague, Rep. Brad Sherman, who has served eight terms. The two Democrats were thrown into the same district by an independent redistricting commission that was tasked with redrawing the state’s lines without regard to partisan edge or seniority.

The district stretches from Hollywood to the San Fernando Valley, and by mid-May the two incumbents, with deep ties to wealthy California fundraising bases, had spent a combined $5.7 million on the race. That figure does not include $550,000 spent on Berman’s behalf by a super PAC.

Despite those millions, nothing is settled. The two Washington veterans — Berman is the top Democrat on the Foreign Affairs Committee, and Sherman is a senior member of the Financial Services Committee — are set to face each other again in November under new election rules that have eliminated party-specific primaries.

In this system, every candidate for a particular seat runs in the same primary, and the two highest vote-getters advance to the November election, no matter which party they hail from. This means that in a district as liberal as the new 30th Congressional District — with just 25 percent of its voters favoring Republicans — the two incumbents were almost certain to advance to the fall ballot.

When Tuesday’s votes were counted, Sherman led his more senior colleague 39 percent to Berman’s 34 percent, and the remaining GOP challengers divided the rest of the vote.

Similar scenarios are possible in several other races, including a contest pitting Democratic Reps. Janice Hahn and Laura Richardson against each other. On Tuesday, Hahn took more than 60 percent of the vote, making her the favorite in the November rematch against Richardson.

This electoral system, already used in Washington state and approved in the final gubernatorial years of Arnold Schwarzenegger (R), is meant to force candidates from each party toward the middle because independents can vote in the open primaries. The former governor thought that in GOP primaries, a small conservative electorate turned out and nominated candidates who had little appeal beyond the 30 percent of the state’s voters who register as Republicans.

“It’s going to push our candidates to be able to broaden their support,” said Rob Stutzman, a GOP consultant and former senior adviser to Schwarzenegger.

In this year’s primaries, independents are still learning the new rules and are not expected to vote in any greater proportion. The most immediate change instituted by Schwarzenegger will be the independently drawn map.

A decade ago, despite controlling all levers of power in Sacramento, California Democrats opted to shore up their own seats in redrawing district lines. The map became the most incumbent-friendly in the nation, virtually impervious to any influence outside the state’s borders. In the ensuing five elections, just one district flipped control (a formerly Republican seat in the Central Valley).

With a 33-to-20 tilt for the Democrats 10 years ago, the state’s current House delegation favors Democrats by 34 to 19.

The new map left a collection of veterans without a political haven, robbing the state of seniority and influence in Washington. Among other retirees, 17-term Rep. Jerry Lewis (R), who steered billions of dollars in military contracts to Southern California, and 16-term Rep. David Dreier (R), chairman of the Rules Committee and a confidant of House Speaker John A. Boehner (R-Ohio), chose to end their careers rather than run long-shot battles against Democrats or fellow Republicans.

But the map has left Democrats optimistic, because several other longtime Republican lawmakers — including seven-term Rep. Gary G. Miller — have been thrown into Democratic-leaning districts.

“It just looks like Democrats are going to pick up a number of seats,” Boxer said.

Several Democrats are also facing their toughest reelection battles in years, how­ever, including seven-term Rep. Lois Capps. Her Santa Barbara-based district reelected her by wide margins the past decade, with a 58 percent tally in 2010 her worst showing.

Capps is already running an aggressive campaign against her likely November challenger, former lieutenant governor Abel Maldonado, a moderate Republican and former state legislator. Maldonado wrote the legislation creating the new election rules.

First, however, he fought off a conservative challenge. In the primary vote, Capps finished with 48 percent to Maldonado’s 33 percent. Actor Chris Mitchum, son of the late actor Robert Mitchum, running with tea party support, had 18 percent.

“This is a whole new game,” Stutzman said.