* Republicans seize control of U.S. House, gain in Senate
* Democrats win in West Virginia, likely to hold Senate
* Economy, discontent with Obama propel Republicans
* Stock index futures turn negative (Adds quotes, details, Boxer wins in California)
By John Whitesides
WASHINGTON, Nov 2 Disenchanted U.S. voters swept Democrats from power in the House of Representatives and strengthened the ranks of Senate Republicans on Tuesday in an election rout that dealt a sharp rebuke to President Barack Obama.
Two years after Obama won the White House, voter anxiety about the economy and discontent with his leadership fueled big Republican gains that toppled Democratic House Speaker Nancy Pelosi from power and ushered in a new era of divided government. [ID:nN31147813] [ID:nN02295573]
Television networks projected Republicans would pick up at least 50 House seats, more than the 39 they need for a majority that would elevate conservative John Boehner to House speaker, put Republicans in charge of House committees and slam the brakes on Obama's agenda.
It was the biggest shift in power at least since Republicans gained 54 House seats in 1994, when Democrat Bill Clinton was in the White House.
"Our new majority will be prepared to do things differently," Boehner told supporters at a downtown Washington hotel. "It starts with cutting spending instead of increasing it, reducing the size of government instead of increasing it, and reforming the way Congress works."
Democrats won key races in West Virginia and California, where networks projected Senator Barbara Boxer would win re-election, ensuring Democrats would retain at least a slender Senate majority.
Republican control of even one chamber of Congress will likely spark legislative gridlock, weakening Obama's hand in fights over the extension of soon-to-expire income-tax cuts and the passage of comprehensive energy or immigration bills.
"The ability of this administration to get major new programs done was already limited. This just seals the deal," said Jaret Seiberg, policy analyst with the investment advisory firm, Washington Research Group.
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U.S. stock futures pulled back from earlier gains as Republican chances of a Senate takeover waned. With opinion polls favoring Republicans, markets had factored in a Republican House win and Senate Democratic hold. [ID:nN02255744]
Investors said the outcome of Wednesday's U.S. Federal Reserve meeting was of greater market importance.
"The Fed's announcement tomorrow is much more critical and really should have much more of the market's focus," said Michael Farr, president of investment firm Farr, Miller & Washington, referring to an expected announcement the Fed will pump billions into the economy to speed the recovery.
In the Senate, Democrats held the late Robert Byrd's seat in West Virginia and Boxer won in California. Republicans picked up Democratic seats in Indiana, Wisconsin, North Dakota and Arkansas.
All 435 House seats, 37 of the 100 Senate seats, and 37 of the 50 state governorships are at stake in Tuesday's voting.
In perhaps the country's most high-profile race, Senate Democratic leader Harry Reid was embroiled in a neck-and-neck re-election fight with Tea Party favorite Sharron Angle in Nevada. He led in early returns.
Florida Republican Marco Rubio and Kentucky Republican Rand Paul became the first Tea Party-backed candidates to win Senate seats, ensuring an influx of conservative views in the staid chamber. Another Tea Party favorite, Republican Christine O'Donnell in Delaware, lost her race.
TEA PARTY RISES
Anger over government spending and economic weakness gave rise to the Tea Party, a loosely organized conservative movement that backed a message of smaller government and lower taxes.
"It's a message that I will carry with me on day one. It's a message of fiscal sanity. It's a message of limited constitutional government and balanced budgets," Paul told supporters in Kentucky.
Television networks said exit polls showed voters were deeply worried about the economy, with eight in every 10 voters saying it was a chief concern, and unhappy with Obama. Four of every 10 voters said they supported the Tea Party, and nearly three-quarters believed government was not functioning properly.
Obama will hold a news conference at 1 p.m. EDT (1700 GMT) on Wednesday to talk about the post-election landscape.
Republican candidates have pushed an agenda of spending cuts and at least a partial repeal of Obama's healthcare and Wall Street reforms, but Obama could veto their efforts.
Stocks in health insurers like UnitedHealth Group Inc (UNH.N), WellPoint Inc WLP.N and Aetna Inc (AET.N) are likely to rise on Republican gains, even if a full repeal of healthcare reform is unlikely.
Voters on Tuesday also weighed in on a variety of topics: in California, for example, they could approve a measure that would legalize possession of marijuana. (Additional reporting by Thomas Ferraro in Washington, Caroline Valetkevitch, Nick Zieminski and Rodrigo Campos in New York and John Rondy in Milwaukee; Editing by Jackie Frank)