WASHINGTON — Three years ago, Massachusetts congressmen Martin Meehan, Stephen Lynch and Edward Markey bucked their state Democratic colleagues and cast votes to give President Bush a green light to go to war in Iraq.

Since then, the three have renounced their votes and emerged as critics of the way Bush has handled the war.

Unlike the dramatic public change of heart by Rep. John Murtha, D-Pa., a decorated Marine veteran who served in Korea and Vietnam, the three congressmen said they began gradually re-evaluating their views soon after the U.S.-led invasion, when no weapons of mass destruction were found.

“The war was based on the false premise that Saddam Hussein had an active nuclear weapons program,” said Markey, who accused the administration of “manipulating facts.”

They are not the first to express regret about their pro-war votes. Several members of Congress, including Reps. Walter Jones, R-N.C., and Robert Wexler, D-Fla., have had changes of heart about Iraq.

But for Meehan, Lynch and Markey, the shift has paid political dividends, helping them mend fences with top state Democratic leaders such as Sen. Edward Kennedy, and anti-war liberals who are active in the party ranks.

“I’d say that we have been the most vocal state delegation in the entire country in criticizing the president’s handling of the war in Iraq,” said Meehan, an early advocate of a phased troop withdrawal.

As Bush’s popularity slumps, public support for the war crumbles and U.S. casualties mount, Democrats nationwide are stepping up their attacks on the president and pressing for a clearer exit strategy.

“There’s been a rift in the Democratic Party about Iraq from the beginning,” said Amy Walter, a congressional expert for the Washington-based Cook Political Report. “As the American public changes its views, it makes it easier for these guys (to change).”

Meehan, Lynch and Markey were among 126 House Democrats who voted for the Iraq war measure one year after the Sept. 11, 2001, terrorist attacks. Their seven Massachusetts House colleagues opposed the resolution, which passed by a vote of 296-133.

Their votes put them at odds with Kennedy, the state’s senior Democrat and one of the party’s leading anti-war voices. The votes also rankled many liberal activists.

Such core support is vital for Democrats seeking to run statewide. Meehan, Lynch and Markey, who were seen as potential Senate candidates when John Kerry ran for president in 2004 and the prospect of an open seat arose, are all considered politically ambitious.

“For those contemplating a presidential effort, this helps to get out in front of that issue three years before the first primaries, so they are on record and not waiting until the primaries to change,” said Earl Black, a Rice University political scientist. “That goes for others who are not running for president as well.”

Back home, the three congressmen drew flak at times for their pro-war votes. Massachusetts is home to an active network of peace groups who have held several protests and vigils denouncing the war. Howard Dean’s rise during the 2004 Democratic presidential primaries also stoked anti-war sentiment across the state. One Boston Common anti-war rally in fall 2002 drew an estimated 15,000 people.

Since none of the three faced major re-election challenges, they had a freer hand than most lawmakers to alter their views on the war.