After Mr. Bush's announcement Tuesday, House Majority Leader Tom DeLay said it would take time to gauge the level of support in Congress for a constitutional amendment. The Republican suggested the difficulty of passing one may cause lawmakers to take a different approach to preserving marriage as a solely man-woman union.
"We don't want to do this in haste," DeLay said.
The front-runner for the Democratic presidential nomination, Sen. John Kerry, and his leading rival, Sen. John Edwards, struggled to make their opposition to Mr. Bush's stance clear as they carefully tiptoed around politically sensitive turf.
Kerry said he supports civil unions, "and I think that that is permissible within state law and it ought to be."
"If he really wants to help married couples, what he should be doing is helping them resolve their economic problems, their health care problems," Edwards said while campaigning in Georgia.
Meeting long-held expectations of his most conservative supporters, Mr. Bush argued that same-sex weddings threaten the institution of marriage — and thus society — and that actions by several local jurisdictions allowing gay marriage make federal intervention the only recourse.
"If we are to prevent the meaning of marriage from being changed forever, our nation must enact a constitutional amendment to protect marriage in America," the president said. "Marriage cannot be severed from its cultural, religious and natural roots without weakening the good influence of society."
Mr. Bush called on Congress "to promptly pass and to send to the states for ratification" an amendment to define marriage as a union of a man and a woman. He had opposed legalizing civil unions as governor of Texas, but Mr. Bush left the door open for states to do so now — an alternative gay rights groups find insufficient.
Mr. Bush's conservative supporters who view prohibiting gay marriage as a priority were thrilled.
"We are delighted the president has stepped forward on this issue and his announcement serves as a critical catalyst to energize and organize those who will work diligently to ensure that marriage remains an institution between one man and one woman," said Jay Sekulow, chief counsel of the American Center for Law and Justice, a law firm founded by the Rev. Pat Robertson.
The federal government and 38 states bar the recognition of gay marriages, but Massachusetts is set to become the first state to sanction gay marriages this spring after its Supreme Court ruled that a ban on homosexual marriage is unconstitutional. The State of Vermont recognizes civil unions of same-sex couples, while San Francisco Mayor Gavin Newsom this month ordered the city to allow same-sex weddings, triggering a wave of legal action against the city.
A majority of Americans — sometimes by as much as a 2-1 margin — oppose legalizing gay marriages. Still, Mr. Bush's move could hold political risks, especially if voters see him as intolerant or question his self-description as a "compassionate conservative."
Democrats promised to fight the amendment and criticized Mr. Bush for wanting to use the Constitution to take away rights. They said he is trying to change the subject from questions on his leadership, the economy, his Vietnam-era military service and the failure to find the weapons of mass destruction he had alleged were in Iraq.
"President Bush is tinkering with America's most sacred document in a shameful attempt to turn our attention away from his record as president," said Democratic National Committee Chairman Terry McAuliffe.
Several Republican lawmakers said they would prefer to see Congress take a different route rather than amend the Constitution.
Republican Rep. David Dreier said he doesn't support a constitutional amendment. "I believe that this should go through the courts, and I think that we're at a point where it's not necessary," he said.
Sen. John McCain said the matter should be left to the states, and Rep. Jerry Lewis said changing the Constitution should be a last resort on almost any issue.
With some conservatives wanting a broader approach than Mr. Bush supports, and others opposing federalizing the issue, DeLay said it's "going to take some time" to unify those groups and examine other options.
"Constitutional amendment — I believe that is the ultimate remedy left for the Congress," he said. "We are looking at other ways of doing it."
The Log Cabin Republicans, a gay Republican group, worried that Mr. Bush risks alienating the 1 million gays and lesbians who voted for him in 2000 by pushing for the constitutional amendment.
"We believe that this is a move to start a culture war, fueled and pushed by the radical right, that will end up in George Bush's defeat, and defeat for a lot of good Republicans who are with us on equality," Mark Mead, the group's political director, said in an interview with AP Radio.
The actual chance of an amendment ever being enacted is actually slim, reports CBS News White House Correspondent Bill Plante.
Amending the constitution requires a two-thirds vote of Congress and then approval by the legislatures of three-fourths of the states.
That process takes years, meaning the president's move may have more effect on the election than it ever has on the constitution.
There are 26 amendments to the U.S. Constitution. Twelve were passed in the 20th Century, including measures allowing women and 18-year-olds to vote, establishing and then repealing prohibition, outlawing the poll tax, instituting the income tax, changing how senators are elected and altering when a president serves, for how long and who replaces him.
In recent decades, at least three efforts to amend the constitution have failed: the Equal Rights Amendment for women, an amendment banning flag burning and an amendment requiring a balanced federal budget.