Democrats are bracing for congressional defeat as most polls predicted a day before the U.S. midterm elections that the Republicans will be the big winners.

U.S. voters go to the polls on Tuesday to decide on all 435 congressional seats, 37 Senate seats and 37 governorships.

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U.S. President Barack Obama makes a final get-out-the-vote push for Democratic candidates during a rally at Cleveland State University. ((J. Scott Applewhite/Associated Press))

A Republican takeover of the House seems all but assured, according to polls, and some predicted the GOP could also have a chance at taking the Senate.

Adding to the Democrats' woes, the Republicans are also expected to win the majority of governorships up for grabs.

The Republicans need a net gain of 39 seats to take control of the House and 10 seats in the Senate to take over that chamber.

Over the weekend, U.S. President Barack Obama pleaded with Democrats to vote.

"Don't let anybody tell you this fight isn't worth it," Obama told the friendly crowd Sunday at Cleveland State University in Ohio. "It's always been hard to bring about change."

Polls predict Republican win

A number of recent polls suggest Republicans are heading for a win in Tuesday's U.S. midterm elections.

A Reuters/Ipsos poll found Monday that 50 per cent of likely voters would choose a Republican candidate, compared to 44 per cent who would pick a Democrat.

According to the poll, the GOP would take over the House but the Democrats would hang on to the Senate by a close margin.

A USA Today/Gallup Poll, 55 per cent of those surveyed said they plan to vote for Republicans, compared to 40 per cent for the Democrats.

A Pew Research Center survey showed the Republicans ahead 48 per cent, compared to 42 per cent for the Democrats.

Obama warned that Republican wins could mean a rollback of the progress he said they had made over the last couple of years.

"It's up to you to remember that this election is a choice between the policies that got us into this mess and the policies that are leading us out of this mess," Obama said.

On Monday, the Democratic National Committee was airing a new ad across the country that features Obama warning of record cuts in education and rollbacks in financial accountability if Republicans take control of Congress.

The Republicans have indicated they will try to undo some of Obama's accomplishments, including health-care reform and financial regulations. But Obama still has the power of the presidential veto, leading many observers to predict gridlock over the next couple of years.

But Republican National Committee chairman Michael Steele dismissed concerns of government gridlock if Republican lawmakers refuse to compromise with Democrats on issues such as deficit spending and taxation.

"We're hoping now for a fresh start with the American people," said Steele. "If we don't live up to those expectations, then we'll have a problem in two years."

With files from The Associated Press