Republicans lost a seat in the Senate in Tuesday's elections, boosting Democratic prospects for keeping control of the upper chamber even as they had little hope of capturing the House of Representatives.

Democrats were counting on the victory in Maine by independent Angus King as they looked to protect their 53-47 advantage in the Senate, where 33 of the 100 Senate seats were at stake in Tuesday's vote. Only a dozen Senate votes _ including Maine _ were seen as competitive.

All 435 House seats were on the ballot, but Republicans were expected to keep control of the chamber, despite the possibility of some Democratic gains.

That means the winner of the presidential vote _ President Barack Obama or Republican Mitt Romney _ will likely face a divided Congress that would make passing any major pieces of legislation difficult.

Republicans had seemed poised to snatch control of the Senate from the Democrats, who were defending 23 seats and losing several retiring veterans. But Republican prospects were undermined by a firestorm that erupted after their candidates in Indiana and Missouri made explosive comments about abortion, rape and pregnancy, and the surprise retirement of Sen. Olympia Snowe in Maine.

Snowe voiced her frustration with the gridlocked Congress when she announced her retirement earlier this year. King, a former governor, won a three-way race to replace her.

King has vowed to be a bridge between the parties and has not said whether he would caucus with Democrats or Republicans and the outcome of the presidential election is certain to have a bearing on any decision. However, he was expected to side with the Democrats after Republican groups spent hundreds of thousands of dollars attacking him.

In Connecticut, Democratic congressman Chris Murphy won the seat being vacated by retiring Independent Joe Lieberman. Vermont's Independent Sen. Bernie Sanders was re-elected, as expected.

Four Democrats senators have also won re-election: Bill Nelson in Florida, Sheldon Whitehouse in Rhode Island, Ben Cardin in Maryland and Tom Carper in Delaware. Republican Sen. Bob Corker was re-elected in Tennessee. Only the race in Florida was competitive.

Democrats were expected to retain control of the Senate but would remain nowhere near the 60-vote supermajority needed to easily pass legislation under Senate rules. Republicans were expected to retain their solid advantage in the House.

Congress consistently rates low in public opinion surveys, but incumbents still tend to get re-elected. They benefit from a system that gives them huge financial advantages in their re-election bids, and enjoy support from voters who tend to favor their own lawmakers even if they dislike Congress overall. Many incumbents in the House are also helped by the once-a-decade redrawing of district boundaries, which has just been completed.

After the Senate races are decided, retiring moderates in Maine, Connecticut, Nebraska, North Dakota, Virginia and Indiana will be replaced, while moderates on the ballot in Montana and Massachusetts could also be gone.

In the Northeast, Republicans could be left with only a few Senate seats. Along with Maine, Massachusetts was vulnerable. Republican Sen. Scott Brown, who managed to win the seat once held by the late Sen. Edward M. Kennedy, now trails Democrat Elizabeth Warren, who is hailed by liberals for her work as a consumer advocate.

In Indiana, moderate veteran senator Dick Lugar had been expected to easily win re-election, but he lost a Republican primary to state treasurer Richard Mourdock, who was backed by the anti-tax, limited government tea party movement. Mourdock has come under withering criticism after saying in a debate that when pregnancy results from rape, it is ``something God intended.'' That opened the way for moderate Democratic congressman Joe Donnelly, who has pulled ahead in recent polls.

In Missouri, Sen. Claire McCaskill had been considered the most vulnerable Democratic incumbent. But another tea party-backed candidate, congressman Todd Akin, won the Republican primary. Akin was disowned by Republican leaders, including Romney, after he remarked in August that women's bodies have ways of avoiding pregnancy in cases of what he called ``legitimate rape.'' McCaskill has since pulled ahead in the polls.

Some tea party favorites are expected to win Senate races, however, including Republicans Deb Fischer in Nebraska and Ted Cruz in Texas. Former Nebraska governor and senator Bob Kerrey has been gaining ground, but Fischer still leads in the race to replace moderate Democratic senator Ben Nelson, who decided to retire.

The closest Senate races could be in the conservative western states of Montana and North Dakota. Republicans hope congressman Denny Rehberg will defeat Sen. Jon Tester, who won a close race during the Democratic wave election of 2008. In North Dakota, Republican congressman Rick Berg is the slight favorite to defeat former state attorney general Heidi Heitkamp for the seat held by retiring Democratic Sen. Kent Conrad.

If Democrats retain control of the Senate, it would give them a firewall against Republican attempts to overturn Obama's signature legislative achievement, his health care reform law, before it is fully implemented in 2014. If Republicans manage to gain control of the Senate, they have promised to repeal the law.

Democratic Senate Majority Leader Harry Reid and Republican House Speaker John Boehner were likely to remain leaders of their chambers. (AP)