WASHINGTON -- President Bush said Wednesday that marriage should be between a man and woman, and that White House lawyers were looking at legislation that in effect would deny gay men and lesbians the right to marry.

But Bush also called on Americans to be tolerant.

"I think it is very important for our society to respect each individual, to welcome those with good hearts, to be a welcoming country," he said during a wide-ranging, solo news conference, his first since before the start of the Iraq war in March.

Even so, the president said that did not mean he had to accept gay marriage. "I believe in the sanctity of marriage," Bush said. "I believe a marriage is between a man and a woman, and I think we ought to codify that one way or the other."

A senior White House official said the president meant that the administration was considering supporting a GOP proposal to amend the Constitution to limit marriage to a man and a woman.

Bush's comments follow advances in the courts for gay rights and some recent polls that show public support for same-sex unions has waned. His words generated swift reaction.

"We are very disappointed that the president is trying to further codify discrimination against gays and lesbians into law," said Winnie Stachelberg, political director of the Human Rights Campaign, the nation's largest lesbian and gay political organization.

"Marriage should be between a man and woman. President Bush has the courage to say it," said Roberta Combs, head of the Christian Coalition of America.

Last month, the Supreme Court threw out a Texas ban on consensual gay sex, and Canada's highest court ruled Ontario could allow same-sex marriages, a decision that generated much discussion in the United States.

In a USA TODAY/CNN/Gallup Poll this week, 57% opposed same-sex civil unions, the most since the question was first asked in 2000. Civil unions give same-sex partners legal rights but don't constitute marriage. Forty percent supported such unions. Also, 50% favored an amendment, and 45% opposed. Administration officials said no decision was likely to be made on whether the president would back an amendment until legal challenges are resolved in New Jersey and Massachusetts, where gays have sued for the right to marry.

Patrick Guerriero, executive director of Log Cabin Republicans, the nation's largest gay Republican organization, said the 1996 Defense of Marriage Act signed by President Clinton already limits marriage to men and women. The act prohibits federal recognition of gay marriage and allows states to ignore same-sex unions licensed elsewhere.

Bush was also asked about his view toward gays. "I am mindful that we're all sinners, and I caution those who may try to take the speck out of the neighbor's eye when they've got a log in their own," Bush replied, paraphrasing from the Bible.

Rep. Jan Schakowsky, D-Ill., sent a letter to the president complaining that he "seemed to equate homosexuality with sin." Rep. Tammy Baldwin, D-Wis., who is openly gay, said she also was troubled by Bush's comments. "Politicizing the Constitution is a terrible precedent."

White House spokesman Scott McClellan said Bush was not trying to insult gays. "The president is someone who does not believe in casting stones."