WASHINGTON (Reuters) - Republicans enter the final week of a bitter election campaign as heavy favorites to win control of the House of Representatives and score big Senate gains, dealing a severe blow to President Barack Obama two years after he entered the White House.
A thirst for change in Washington and worries about the stumbling economy appear likely next Tuesday to break Obama's Democrats' grip on Congress in a potential rout that would topple House Speaker Nancy Pelosi from power.
With more than 90 Democratic-held seats at risk on November 2 in the 435-member House, independent analysts project Republicans will pick up at least the 39 Democratic seats they need for control.
Republicans are also headed to big gains in the Senate but are expected to fall short of picking up the 10 Democratic seats needed for a majority. To control the 100-member Senate, Republicans will need to sweep nearly every competitive race -- a difficult but not impossible task.
A Republican win in the House and gains in the Senate would likely put the brakes on Obama's agenda and spark a prolonged period of legislative gridlock, analysts said. Investors expect a split government and have largely factored in the result, so a dramatic move in stocks on November 3 is unlikely without an unexpected showing by either party.
White House spokesman Robert Gibbs said Obama cast an absentee ballot on Tuesday for the U.S. Senate and governor races in the president's home state of Illinois.
Dozens of races in both chambers are too close to call, and party committees and outside groups have poured millions of dollars into last-minute advertising buys to sway an electorate that has been in an anti-Washington mood all year.
"I haven't seen anything that makes me think there will be a drastic change in the public mood or trends in the next week," Republican strategist Kevin Madden said. "It feels like the concrete was poured on the major issues months ago."
All 435 House seats, 37 Senate seats and 37 of 50 state governorships are at stake on Tuesday.
Democrats have been on the defensive all year from Maine to California over Obama's plunging popularity, growing federal budget deficits and their support for an economic stimulus package, industry bailouts and a sweeping healthcare overhaul.
Republicans are also projected to win a majority of the 37 governors' races, giving them an edge in the once-a-decade process of redrawing congressional district boundaries that begins next year.
Democrats have been heartened by a slight upturn in polls measuring the enthusiasm of their core supporters in recent weeks, and by early voting results showing Democrats casting more ballots than Republicans in key states.
"The Democrats will hold the Senate and the town will be more Republican than it was. These are things we know," said Simon Rosenberg, head of the Democratic advocacy group NDN.
"But the idea that somehow Republicans have already won the House is sort of ridiculous. It's a likely outcome, but it's not a foregone conclusion. Mistakes can be made, bad ads can be aired -- there are a lot of close races," he said.
History is with Republicans, as the party holding the White House traditionally loses seats in a president's second year.
Obama's approval rating has dipped into the low to mid-40s, near President Bill Clinton's mid-40s rating when his Democrats lost 54 House seats in 1994. Huge majorities of voters believe the country is on the wrong track.
Republicans expanded the number of competitive Democratic House districts in the final month of the campaign, putting dozens of once safe Democratic-held seats in play.
"A few weeks ago, we found ourselves on the precipice of victory. Now we are closing the deal," Pete Sessions, head of the Republican House campaign committee, said in a memo to reporters. "Nancy Pelosi's days as speaker of the House are numbered."
In the Senate, Republicans appear likely to hold all of their own seats, although the race in Kentucky has tightened. They also have commanding poll leads in three Democratic-held states -- Arkansas, Indiana and North Dakota -- and a solid lead in Wisconsin.
That means for a majority, Republicans must string together wins in six of seven close races in California, Washington, Nevada, Colorado, Pennsylvania, Illinois and West Virginia.
A Reuters-Ipsos poll on Tuesday found the Senate race in Pennsylvania, where Republican Pat Toomey once had a sizable lead, is a dead heat after a comeback by Democrat Joe Sestak.
Senator Barbara Boxer in California leads her re-election race and Senator Patty Murray is ahead in Washington in two Democratic-leaning states that Democrats hope will give them the final margin they need to save their Senate majority.
Democrats hope to counter Republican enthusiasm, stoked by activists in the loosely organized Tea Party movement and their agenda of lower taxes and lower spending, with a strong voter turnout effort.
Obama has hit the road to help get out the vote and will spend this weekend on a whirlwind campaign trip in Connecticut, Illinois, Pennsylvania and Ohio.
But Republicans say there is no time left for a dramatic shift in the electorate.
"This election seemed settled months ago and little has changed since," Republican strategist Rich Galen said. "I can't conceive of anything that could happen that could turn this around in the House."
According to a Reuters poll, a majority of analysts expect a Republican takeover of at least one chamber will result in near-term equity gains.
"The S&P 500 has already put in about 20 to 30 points as a results of the polls shifting in favor of the Republicans, said Jeffrey Friedman, senior market strategist at Lind-Waldock in Chicago. "If they don't get those gains, those points will be taken out."
Editing by Philip Barbara and Will Dunham