Washington - Democrats increased their control of Congress in elections Tuesday, picking up significant gains in the Senate and House of Representatives by capitalizing on a backlash against Republicans and President George W Bush.

The Democrats won three seats vacated by retiring Republicans in Virginia, New Mexico and Colorado, while Democratic challengers ousted two of their Republican opponents in New Hampshire and North Carolina.

Democrats were also hopeful about knocking off the Republican minority leader in the Senate, Mitch McConnell, an outcome that would be a major blow to Republicans. But McConnell sewed up a narrow victory over Democrat Bruce Lunsford.

The Democrats were optimistic hopeful they could expand their control of the Senate from a slim 51-49 margin that includes two independents who vote Democratic. They gained five seats to climb to a 56-40 majority with four races still undecided. But it appeared they would fall short of the 60 needed to prevent Republicans from blocking votes.

"I'm particularly delighted that, although the results are not all in tonight, that it looks like we're going to be increasing our majorities in the House and in the United States Senate," said Nancy Pelosi, the House speaker and top Democrat on Capitol Hill.

In Virginia, former Democratic governor Mark Warner defeated a former Republican governor, James Gilmore, to take the seat occupied by Republican Senator John Warner, who is retiring at the end of his term and is not related to his successor.

Democratic challenger Kay Hagan defeated Republican Senator Elizabeth Dole in North Carolina, while John Sununu, a Republican senator, was ousted by Democratic challenger Jeanne Shaheen.

And in New Mexico, Democrat Tom Udall took the seat occupied by longest-serving Republican Pete Domenici, who is also retiring, while his cousin in Colorado, Mark Udall, won another seat occupied by a departing Republican.

In the House, Democrats had so far picked up 11 seats to increase their majority from 236 to 247, while Republicans had won 166 seats with 22 races still undecided.

Heading into the election, the Democrats controlled the 100-seat Senate 51-49 and the House of Representatives with a 236 to 199 majority.

All 435 seats in the House were up for grabs, while about one- third of the Senate stood for election.

In Minnesota, comedian and Democratic challenger Al Franken was running neck-to-neck with Republican incumbent Norm Coleman. Coleman was holding a razor-thin 
2,000 vote lead over Franken with 95 per cent of voting precincts tallied.

Senator Joe Biden, Barack Obama's vice presidential candidate, handily won re-election in Delaware. With Obama's victory Biden will have to vacate his seat, but would likely be replaced by a Democrat appointed by the state's governor.

Democrats were also hopeful of defeating Alaska Senator Ted Stevens, the longest serving Republican, following his conviction last week on corruption charges. Stevens was clinging to a 48-47 per cent lead over Democrat Mark Begich with 65 per cent of precincts reporting.

There were at least a couple of notable Democrats who survived tight races. Louisiana Senator Mary Landrieu survived a tough challenge, while long time Representative John Murtha prevailed in a race where he was believed to be vulnerable.

Murtha, a former Marine and Vietnam War veteran, had weeks ago commented that Obama night not win his congressional district because it was racist. He committed a second blunder while trying to backtrack on his remarks, but then referred to many of his constituents as "red necks." (dpa)