Democrats made big gains in both the U.S. Senate and House last night, picking up dozens of Republican seats and expanding their congressional majority.

A dismal economy and an unpopular president weighed heavily on GOP incumbents across the country, and Democratic candidates rode the coattails of Sen. Barack Obama's presidential campaign to compete in states and districts that voted overwhelmingly for President Bush just four years ago.

The party won Senate victories in New Hampshire, Virginia, New Mexico, Colorado and North Carolina, where Democratic newcomer Kay Hagan defeated prominent GOP Sen. Elizabeth Dole.

In Minnesota, Republican Sen. Norm Coleman held a narrow lead over Democrat Al Franken, the former "Saturday Night Live" writer and actor. Sen. Gordon Smith, R-Ore., trailed Democrat Jeff Merkley in another tight race.

The GOP held off a tough challenge in Kentucky.

In Alaska, Sen. Ted Stevens -- the longest serving Republican senator in U.S. history -- was locked in a tight contest, after he was convicted last week of seven counts of lying on Senate financial disclosure forms.

Senate Democrats appeared likely to fall short of the 60-seat, "filibuster-proof" majority that would allow them to limit floor debate and pass major legislation over the objections of Republican senators.

But the majority party is still poised to wield considerable power in the Senate, and Democratic lawmakers will no longer face veto threats from President Bush.

That would be a sharp departure from the past two years, when Senate Democrats contended with a razor thin, two-seat hold on power that depended on the support of a pair of independents, including Sen. Joseph Lieberman of Connecticut, a backer of Sen. John McCain's presidential campaign.

Democrats yesterday also made sizable gains in House races.

In Pennsylvania, GOP Rep. Phil English, a veteran Erie lawmaker, lost to Democrat Kathy Dahlkemper. Meanwhile, two prominent Pennsylvania Democrats, Rep. John Murtha, of Johnstown, and Paul Kanjorski, of Luzerne, fended off the toughest political challenges of their long careers.

Mr. Kanjorski, serving his 12th term, defeated Republican Lou Barletta, the mayor of Hazleton who attracted national headlines as a champion of anti-immigration legislation in his northeastern Pennsylvania city.

Freshman Rep. Jason Altmire, D-McCandless, pushed back a challenge from Republican Melissa Hart, whom he defeated in 2006 to take his seat in a district covering Pittsburgh's North Hills and parts of Beaver County.

Rep. Tim Murphy, R-Upper St. Clair, defeated businessman Steve O'Donnell, holding onto his seat in a largely suburban district south and east of Pittsburgh.

Three Democratic freshmen from the eastern part of the state -- Patrick Murphy, Chris Carney and Joe Sestak -- all won re-election.

Democrats also won House races in Florida, New York and Connecticut, where Rep. Chris Shays lost the only remaining GOP seat in New England.

The Republicans picked up one Florida seat when attorney Tom Rooney defeated first-term Democratic Rep. Tim Mahoney, who had admitted to two extramarital affairs just weeks before Election Day. Mr. Rooney is a grandson of the late Steelers patriarch Art Rooney.

But overall Democratic gains helped build on the performance in the 2006 midterm elections, when the party took control of both chambers of Congress for the first time since 1994.

Democratic candidates undoubtedly benefited from the Obama campaign's huge war chest and formidable ground organization, built over a nearly two-year period.

In Virginia, popular former Democratic Gov. Mark Warner easily defeated another former governor, Republican Jim Gilmore, for the Senate.

Another former Democratic governor, Jeanne Shaheen, beat Sen. John Sununu in New Hampshire in a rematch of their 2002 race.

Mrs. Dole, the wife of former GOP presidential candidate Bob Dole, lost in North Carolina, where the Obama campaign and the national Democratic Party invested huge sums of time and money.

Democrats also proved successful in two western states that went for President Bush in 2004. In Colorado, Democratic Rep. Mark Udall, son of the late Arizona Rep. Morris "Mo" Udall, defeated former Republican Rep. Bob Schaffer for the seat now held by Republican Wayne Allard. And in New Mexico, Democratic Rep. Tom Udall -- a cousin of the Colorado Udall -- was successful against Republican Rep. Steve Pearce. He will succeed retiring Republican Sen. Pete Domenici.

Democrats also took sharp aim at Senate Minority Leader Mitch McConnell of Kentucky, but the GOP incumbent fought back a challenge by businessman Bruce Lunsford in a costly race.

Going into the election, only one incumbent Democrat had appeared vulnerable: Sen. Mary Landrieu of Louisiana. Republicans made a spirited run at her, but she easily won reelection.