Civil rights leader John Lewis has dropped his support for Hillary Rodham Clinton's presidential bid in favor of Barack Obama.

Lewis, a Democratic congressman from Atlanta, is the most prominent black leader to defect from Clinton's campaign in the face of near-majority black support for Obama in recent voting. He also is a superdelegate who gets a vote at this summer's national convention in Denver.

''After taking some time for serious reflection on this issue, I have decided that when I cast my vote as a superdelegate at the Democratic convention, it is my duty as a representative of the 5th Congressional District to express the will of the people,'' Lewis said in a statement. ''As a U.S. representative, it is my role not to try to subdue or suppress the will of the people, but to help it prosper and grow.''

Lewis' constituents supported Obama roughly 3-to-1 in Georgia's Feb. 5 primary. His endorsement had been a coveted prize among the Democratic candidates thanks to his standing as one of the last major civil rights leaders of the 1960s.

Lewis said he had tried to contact Clinton.

''I think the candidacy of Senator Obama represents the beginning of a new movement in American political history that began in the hearts and minds of the people of this nation,'' he said. ''And I want to be on the side of the people, on the side of the spirit of history.''

Sen. Byron Dorgan of North Dakota endorsed Obama on Wednesday, citing his record on trade.

''Senator Obama has never felt ... that NAFTA was good for America,'' Dorgan said in a campaign conference call with reporters.

Dorgan said Obama has supported key trade issues. ''He and I feel the same way. We both believe in trade and plenty of it. We just insist it that it be fair to our country _ the rules be fair.''

NAFTA, the free trade agreement with Canada and Mexico, is unpopular with blue-collar workers whose votes are critical in the Democratic primary Tuesday in Ohio.

Obama has won 11 straight primaries and caucuses since Super Tuesday, increased his advantage in the all-important delegate count and has attracted the support of his congressional colleagues. On Tuesday, he secured the endorsement of one-time presidential candidate Sen. Chris Dodd of Connecticut.

Clinton has been endorsed by 13 of her Senate colleagues, Obama 10.

Dorgan was an ally of former President Clinton and a vocal critic of President Bush. As chairman of the Democratic Policy Committee, he has led hearings on government accountability issues related to the Iraq war and hurricanes on the Gulf Coast.

Dorgan has built a reputation for championing populist farm programs, criticizing Republican free-trade policies and assailing big business. He made headlines in 2005 when he called for a windfall profits tax on major oil companies.

Last year, he authored a measured to block funding of a Department of Transportation pilot program required under NAFTA that would have opened the U.S. to cross-border long-haul Mexican tractor trailers. The program was opposed by the Teamsters Union, among others.

Source: Associated Press