SAN FRANCISCO (AP) — Federal observers traveled from Washington to Sacramento on Thursday to ensure every vote is counted in a congressional race near the state capital, one of three U.S. House contests in California too close to call two days after the most hotly contested congressional elections the state has seen in decades.

As candidates in Sacramento, San Diego and Palm Springs waited out the slow dribble of news about the ongoing vote count, national Democrats and Republicans kept a close eye on the contests, eager to pick up seats in the state's largest-in-the-nation congressional delegation.

The three California contests were among eight House races nationwide with margins too slender for The Associated Press to declare winners as thousands of mail-in and provisional votes remained to be counted.

In California's 7th House District located in the Sacramento suburbs, Republican Rep. Dan Lungren trailed his Democratic opponent Ami Bera by just 184 votes out of 176,000, giving it the closest margin of all eight undeclared contests.

"I'm very confident that the ballots that will come in the next few days will go in our favor," Bera said.

Countered Lungren: "If anybody tells you they know the outcome of this, they're smoking something."

Elsewhere in California, longtime Republican Rep. Mary Bono Mack was facing an uphill battle to retain her seat in Palm Springs after a spirited challenge by Democrat Raul Ruiz, a Harvard-educated physician who proved adept at mobilizing the district's growing swath of Hispanic voters. She trailed by about 4,500 votes out of more than 162,000 cast.

Another Republican incumbent, Brian Bilbray from District 52 in San Diego, also trailed. Following an updated tally Thursday, Democrat Scott Peters stretched his lead to 814 out of more than 210,000 ballots.

In Sacramento, four staffers from the U.S. House Administration Committee — two from each party — arrived Thursday morning to oversee the vote counting, Lungren spokesman Jeff Wyly said. The congressman recused himself from the committee's effort because he is the chairman.

Steve Dutton, a spokesman for the committee, did not immediately offer details about the staffers' involvement in the race or disclose whether staff had been deployed to other districts where the outcome is uncertain.

California's congressional races have grown much more competitive since an independent panel redrew the district boundaries two years ago, which coincided with the year the U.S. Supreme Court struck down limits on outside political spending.

California law gives county registrars 28 days after the election to finalize results, but any candidate or voter can ask for a recount within the following five days. If that happens, local elections officials can appoint four voters to oversee a special recount board, a process that could take weeks to finalize.

Before Tuesday's election, California's congressional delegation had 33 Democrats, 19 Republicans and one vacancy in a Democratic district. With three races still to be called, the delegation is 35 Democrats and 15 Republicans.

The GOP has been hit by twin forces in California — a declining number of voters registered as Republican and independent redistricting, which meant some GOP incumbents faced vastly different constituencies than when they were first elected.

If Democrats successfully oust all three Republican incumbents in California, it would affect not only the makeup of the House this year but give the party a strategic boost for the midterm elections in 2014, when Democrats stand a chance at retaking a majority, said Jesse Ferguson, a spokesman for the Democratic Congressional Campaign Committee.

"Our gains in California are the fuel behind our gains across the country," Ferguson said.

A spokesman for the National Republican Congressional Committee did not immediately return a call seeking comment.