The contest for the White House between President Bush and likely Democratic presidential nominee, Senator John Kerry, spilled into the U.S. Congress Thursday as Republican lawmakers launched a rare unified attack on the floor of the House of Representatives against Mr. Kerry's criticism of U.S. involvement in Vietnam more than 30 years ago.

Republicans used a speech period before legislative business to renew charges Mr. Kerry was "unpatriotic" when he criticized U.S. troops in Vietnam after he left military service.

They were referring to testimony by Mr. Kerry in 1971 to the Senate Foreign Relations Committee.

Republican Congressmen John Kline and Joe Wilson were among six Republicans who took to the floor to lash out at Mr. Kerry.

Kline: "Thirty-three years ago today he stood before the Senate Foreign Relations Committee disparaging, disparaging our brave service men and women as murderers, yet today in pursuit of the presidency of what he called "a hypocritical nation" he boasts of his service alongside them."

Wilson: "Many veterans, including myself as a veteran, view John Kerry's testimony that day as one of the worst public slanders ever against the valor and character of the American military."

The ferocity of the attacks appeared to take Democrats by surprise. Initially only three came to Mr. Kerry's defense, among them Congressman John Larson.

"A decorated veteran in Vietnam," he said. "A person who received three purple hearts and the silver star for serving with distinction and now because he is a candidate for president of the United States he receives the unbridled attack of the opposition."

By the end of the day Thursday, Democrats had re-grouped, sending eight of their own to defend Mr. Kerry. "Something happened on the floor of the House this morning that in my judgment is shameful, shameful," said Rep. Ted Strickland. "Because the record of an American hero, who shed his blood, who earned three purple hearts, a silver star and a bronze medal, was referred to on the floor of this House as 'Hanoi John.' Is that what we have come to in this House! "

Personal attacks on members of the Senate violate House rules, and Republican Congressman Ray LaHood who was presiding at the time admonished members on that point.

However, Democrats' attempts to press on the issue resulted in this exchange between Mr. LaHood and Georgia Democrat John Lewis.

Lewis: "Is it proper, is it appropriate, is it a violation of the House rules for members to attack members of the other body [Senate] by name?"

LaHood: "Ah, when a member of the Senate is a candidate for president, it is proper and fair to speak about the member's record, but not to make personal attacks."

Lewis: "It is my understanding that this person is not even a nominee of his party yet."

LaHood: "The chair can't rule on that. The chair is not going to rule on who the nominee is."

Mr. Kerry has used support by some war veterans groups to bolster his presidential campaign.

The latest criticisms of his decades-old comments on Vietnam come as Republicans attempt to portray him as inconsistent on key issues, including defense and support of the military, and amid some suggestions in the media his campaign for the White House has been "losing its focus."

President Bush, too, continues to be pressured by problems facing the U.S. occupation of Iraq, and some opinion polls showing him losing ground to Mr. Kerry on the issue of Iraq and national security.