Washington - One day after congressional elections, four races in the Senate remained undecided Wednesday and the outcome in a handful of contests in the House of Representatives were still uncertain.

But it was clear that Democrats had widened their majorities in both chambers.

Democrats capitalized on the backlash against Republicans and President George W Bush to pick up seats. The Democrats won three Senate 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.

With four races still undecided in Alaska, Georgia, Minnesota and Oregon, Democrats have increased their majority to at least 56 seats in the 100-seat chamber when the next Congress convenes in January. That majority includes two independents who normally vote with the Democrats.

It appeared unlikely, however, that Democrats would claim all of the four remaining undecided seats - support they would need to reach the 60 seat majority needed to prevent Republicans from blocking votes.

In the House, Democrats had picked up at least 18 seats by early Wednesday to increase their majority from 236 to 254, while Republicans had won 173 seats with 8 races still undecided, CNN reported. NBC News projected the Democrats would end up with 258 seats.

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 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 in New Hampshire.

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 Minnesota, comedian and Democratic challenger Al Franken was running neck-and-neck with Republican incumbent Norm Coleman in a race that could be headed for a recount. Coleman was holding a razor-thin edge over Franken.

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. The race against Democrat Mark Begich remained too close to call Wednesday evening.

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

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