WASHINGTON — Democrats fattened their majority control of the Senate yesterday, ousting Republican Sens. Elizabeth Dole of North Carolina and John Sununu of New Hampshire and capturing seats held by retiring GOP senators in Virginia, New Mexico and Colorado.

Piggybacking on the excitement level raised by presidential victor Barack Obama and his voter-registration and get-out-the-vote drives, Democrats increased their effective majority to at least 56 seats in the 100-member Senate.

They did not turn over a single seat to Republicans. All Democratic incumbents on the ballot prevailed.

Four races with Republican incumbents remained to be resolved — in Alaska, Oregon, Minnesota and Georgia.

But Republicans stopped a complete rout, holding the Kentucky seat of Senate Minority Leader Mitch McConnell and a Mississippi seat once held by Trent Lott.

North Carolina state Sen. Kay Hagan, little known politically before her run, defeated Dole — a former Cabinet member in two Republican administrations and 2000 presidential hopeful. Dole had tried to tie Hagan, a former Presbyterian Sunday school teacher, to atheists in an ad that backfired.

"What we were able to accomplish in a little more than a year is a testament to how hungry people are for change," Hagan told a victory rally in Greensboro.

In New Hampshire, former Democratic Gov. Jeanne Shaheen defeated Sununu in a rematch of their 2002 contest.

In a pair of western races, Reps. Tom and Mark Udall took over Senate seats held by retiring Republicans. Tom Udall, the son of former Interior Secretary Stewart Udall, defeated Republican Rep. Steve Pearce to succeed Pete Domenici in New Mexico. Tom's cousin Mark, the son of the late Rep. Morris Udall of Arizona, won the Colorado seat held by Republican Wayne Allard, who did not seek re-election.

Former Democratic Gov. Mark Warner breezed to victory in Virginia to take a Senate seat held for five terms by retiring GOP Sen. John Warner, beating another former governor, Republican Jim Gilmore. The two Warners are not related.

Democratic vice presidential candidate Joe Biden won another six-year term representing Delaware in the Senate. It became moot when Obama won the presidential election.

Democratic Sen. Mary Landrieu of Louisiana, the only serious GOP target, won her re-election over Republican state treasurer John Kennedy.

McConnell, the Senate Republican leader, had been a target of national Democrats after leading successful filibusters against much of their legislative agenda the past two years. He won re-election against two-time Democratic gubernatorial candidate Bruce Lunsford in a contentious race.

In a tight Mississippi contest, Republican Roger Wicker defeated former Democratic Gov. Ronnie Musgrove to serve another four years of the term originally won in 2006 by Lott. Wicker was appointed to the post temporarily after Lott stepped down.

Democrats had counted on a slumping economy, an unpopular war and voter fatigue after eight years of President Bush to bolster a razor-thin 51-49 effective majority they've had the past two years after adding six seats in 2006.

They set a sky's-the-limit goal of controlling 60 Senate seats when the new Congress convenes in January — the magic number needed to prevent Republicans from blocking bills and judicial nominees. It was always a long shot.

But having a majority in the high 50s will enable Democrats to exercise far more control than they have now, since some Republicans probably will join them in efforts to break Senate logjams on many bills and judicial appointments.

Included in the Democrats' majority are two holdover independents, Sen. Bernie Sanders of Vermont and Sen. Joe Lieberman of Connecticut, who have voted with them for the most part over the past two years.

Democrats will lose two incumbents: Obama and Biden. But Democratic governors in Illinois and Delaware are sure to appoint Democrats to replace them.

Democrats had fewer seats to defend than Republicans. Of the 35 races on yesterday's ballot, 23 were held by Republicans, 12 by Democrats.

Another possible pickup for Democrats: Sen. Ted Stevens, R-Alaska. Stevens, at 84, the longest serving Republican in Senate history, sought re-election despite calls from GOP leaders to resign after he was convicted last week of seven counts of lying on Senate financial disclosure forms.

He was locked in a tight contest with Democrat Mark Begich, the mayor of Anchorage. Another closely contested race was in Minnesota, where Republican incumbent Norm Coleman was challenged by Democrat Al Franken, the former "Saturday Night Live" writer and actor.

Republican Sen. Gordon Smith in Oregon was also on the list of Democratic targets.

Republicans retained the Nebraska seat of retiring Sen. Chuck Hagel, with former Gov. Mike Johanns defeating Democrat Scott Kleeb, a college history instructor.

Republicans also kept the Idaho seat of Sen. Larry Craig, who decided not to run for re-election after he was caught last year in a men's room sex sting. Idaho Lt. Gov. Jim Risch won the seat.