President George W. Bush called Tuesday for an amendment to the U.S. Constitution defining marriage as a union only between a man and a woman.

Opponents of the plan quickly reacted, saying Bush was encouraging making discrimination part of the foundation of the nation's laws.

Bush blamed what he calls activist judges and some local officials for creating confusion about "the most fundamental institution of civilization," and said the move was needed to provide clarity.

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He called the ruling earlier this year by Massachusetts' highest court that the state could not prevent same-sex couples from marrying, and that some form of civil unions would not alleviate the discrimination, an "aggressive attempt to redefine marriage."

Those rulings led the state to consider several constitutional amendments, though the Legislature could not agree on language.

He said that situation, as well as San Francisco's decision to issue thousands of marriage licenses to homosexual couples -- an act the city's mayor described as civil disobedience against a state law banning the practice -- "left the people with one recourse," changing the Constitution.

Bush said that the people have overwhelmingly spoken in support of similar definitions, with the passage of the federal Defense of Marriage Act during Bill Clinton's presidency and through similar acts in 38 states.

"The defense of marriage requires a constitutional amendment," he said.

Bush noted that the Constitution's "full faith and credit clause," which generally requires states to recognize marriages from other jurisdictions, could be used by certain areas to change marriage all over.

He also said that the nation needs to respect every person while respecting marriage. He said there was no contradiction between those ideas.

Lawmakers Advocate Go-Slow Approach

Many congressional Republicans are advocating a go-slow approach to the president's call for a constitutional amendment banning gay marriages.

House Majority Leader Tom DeLay says he appreciates the president's "moral leadership" on the issue, but expressed caution about moving too quickly toward a constitutional solution.

While some Republicans urged swift approval of the amendment, others say changing the Constitution should be a "last resort" on any issue.

House Minority Leader Nancy Pelosi vowed to fight any amendment. She says a constitutional amendment has never been used to discriminate against a group of people, adding, "We must not start now."

California Rep. Bob Filner called the president's move a clear case of "wedge politics" designed to divide the country.

Amending the Constitution is not quick or simple. A two-thirds majority of both the House and Senate must pass an amendment, which is then sent to the states for ratification. It must be approved by three-fourths, or at least 38 of the 50 states.

Groups React

A gay Republican group says Bush could end up losing people who had previously supported him.

The Log Cabin Republicans accused Bush of "writing discrimination into the Constitution." The executive director of the group said the president has jeopardized the support of people who voted for him in 2000 and who identified themselves in exit polls as being gay.

"As conservative Republicans, we are outraged that any Republican -- particularly the leader of our party and this nation -- would support any effort to use our sacred United States Constitution as a way of scoring political points in an election year," Patrick Guerriero said.

The group pointed out that there have been no legal challenges to the Defense of Marriage Act.

Democratic National Committee chief Terry McAuliffe calls Bush's announcement purely political. He said attacking gay families as an election strategy is shameful. And a top official with the Human Rights Campaign said the group is confident any amendment will fail.

Seth Kilbourn of the Human Rights Campaign said Bush is using the Constitution to discriminate against families. He said Bush is hurting families for political gain and accuses the president of using the issue to jump start his campaign.

But Family Research Council president Tony Perkins backed Bush, saying he's done the right thing. Perkins said a constitutional amendment is essential to protecting the traditional and historical definition of marriage.

Bush's announcement was applauded by the American Center for Law and Justice, which focuses on family and religious issues. The group says Bush will serve as a "critical catalyst" in efforts to keep marriage traditional.

"The President's announcement is vital to launching the amendment process and efforts to protect marriage. We are grateful for his support on this most important issue," said chief counsel Jay Sekulow.

The ACLJ also supports criminal charges against those who have allowed same-sex marriages in California.