Washington- The issue of gay marriage is causing divisions within the Republican Party, including the highest reaches of the White House.

The split has been so pronounced that President Bush faces strong opposition within his own administration to a constitutional amendment that would outlaw gay marriage. The split has pitted Mr. Bush against his own wife, first lady Laura Bush.

Mrs. Bush has warned that promoting the amendment could backfire against the GOP in congressional races in November. She has suggested that a constitutional amendment would hamper any constructive debate over gay marriage.

“Well, I don’t think it should be used as a campaign tool, obviously,” Mrs. Bush said. “But I do think it’s something that people in the United States want to debate. And it requires a lot of sensitivity to talk about the issue, a lot of sensitivity.”

“People, I have found, over the country don’t want the governor of Massachusetts or the mayor of San Francisco to make the choice for them-the courts of Massachusetts, I should say,” the first lady told Fox News. “So I think it deserves debate. I think it’s something that people want to talk about.”

Administration sources said the split has divided the GOP majority in the Senate. They said that, unless the White House presents a united front, the proposed constitutional amendment will fail in the Senate.

Vice President Dick Cheney, whose daughter is a lesbian, also opposes the bill. Administration sources said Mr. Cheney has argued against introducing a constitutional amendment in 2006.

In 2004, Mr. Cheney’s daughter, Mary, was said to have nearly quit the Bush-Cheney campaign because of the president’s position on gay marriage. Miss Cheney has been touring the talk show circuit and speaking out against the marriage amendment.

“What I can say is look, amending the constitution with this amendment, this piece of legislation, is a bad piece of legislation,” Miss Cheney said. “It is writing discrimination into the constitution, and, as I say, it is fundamentally wrong.”

Sources said the administration has to act quickly as the Senate plans to debate legislation in the first week of June that would define marriage as the union between a man and a woman. Senate Majority Leader Bill Frist and White House Deputy Chief of Staff Karl Rove have been forceful proponents of the legislation.

Both Mr. Frist and Mr. Rove have assessed that the legislation will help mobilize the Christian Right to support GOP candidates for Congress. Recent polls show a sharp drop in support for the administration among conservatives.

“I basically say, Mr. Vice President, right now marriage is under attack in this country,” Mr. Frist said. “And we’ve seen activist judges overturning state by state law, where state legislatures have passed laws defining marriage between a man and a woman, and that’s being overturned by a handful of activist judges around the country. And that is why we need an amendment to come to the floor of the United States Senate to define marriage as that union between one man and one woman.”

On May 18, the Senate Judiciary Committee, in a vote split along party lines, approved a constitutional amendment that banned gay marriage. The committee hearing was marred by a shouting match between Chairman Arlen Specter, Pennsylvania Republican, and Democratic Sen. Russ Feingold of Wisconsin, who walked out of the session.

“I don’t need to be lectured by you,” Mr. Specter told Mr. Feingold. “You are no more a protector of the constitution than am I.”