WASHINGTON (AP) _ In a dramatic victory for gay rights, the Supreme Court struck down a Colorado measure it said would deny homosexuals constitutional protection and make them ``unequal to everyone else.''

Colorado's constitutional amendment, banning laws that protect homosexuals from discrimination, ``identifies persons by a single trait and then denies them protection across the board,'' said Justice Anthony M. Kennedy, writing for the majority in Monday's 6-3 decision.

``It is not within our constitutional traditions to enact laws of this sort,'' Kennedy wrote.

It was the first major ruling involving gay rights since a 1986 decision in which the justices upheld a Georgia law that criminalized homosexual sex between consenting adults.

Monday's ruling did not address the legality of homosexual conduct. It also did not require stricter legal scrutiny of laws based on sexual orientation, as the court has for laws creating classifications based on race or sex.

But the justices said the Colorado amendment denied gays a political right enjoyed by everyone else _ the chance to seek protection from discrimination in employment, housing and public accommodations.

Such anti-discrimination laws do not grant homosexuals special rights, Kennedy said, but give them ``protections taken for granted by most people either because they already have them or do not need them.''

In a stinging dissent, Justice Antonin Scalia accused the majority of ``imposing upon all Americans'' the pronouncement that ``animosity toward homosexuality ... is evil.''

Scalia called the amendment ``Colorado's reasonable effort to preserve traditional American moral values'' and added that it was not the courts' business ``to take sides in this culture war.''

``The amendment prohibits special treatment of homosexuals and nothing more,'' Scalia said.

His dissent was joined by Chief Justice William H. Rehnquist and Justice Clarence Thomas.

Joining Kennedy's majority opinion were Justices John Paul Stevens, Sandra Day O'Connor, David H. Souter, Ruth Bader Ginsburg and Stephen G. Breyer.

President Clinton ``believes today's decision was appropriate,'' said White House spokesman Mike McCurry. He called the Colorado law ``bad policy ... inconsistent with our common values.''

The reaction was also upbeat at a gay and lesbian bookstore a few blocks away.

``I think this is the most significant decision in a decade for gay rights, absolutely,'' said Gene Copello of San Francisco.

Shannon Wyss of Washington said the ruling was only a small step for the gay rights movement as a whole, but ``I think that for this Supreme Court, it's a huge step.''

Colorado Attorney General Gale A. Norton said she was disappointed, adding, ``The debate in Colorado was about whether special rights should be extended to a new group.''

The Colorado constitutional amendment, approved in 1992, has never been enforced because it was immediately challenged in court by gay men and women as well as three cities that had enacted gay rights ordinances.

The amendment would have canceled gay rights ordinances enacted in Denver, Boulder and Aspen and barred the enactment of any other gay rights laws or policies by the state or local governments.

The Colorado Supreme Court invalidated the amendment on the ground it denied homosexuals an equal voice in government.

Voter approval of the amendment led gay rights activists to organize a boycott of Colorado tourism.

Kennedy wrote that one rationale advanced for the amendment was that it protected landlords or employers with personal or religious objections to homosexuality. But he said the amendment did not relate to that purpose.

``The amendment seems inexplicable by anything but animus toward the class that it affects,'' wrote Kennedy. ``A state cannot so deem a class of persons a stranger to its laws.''

Suzanne B. Goldberg of the Lambda Legal Defense and Education Fund said Monday's ruling ``says that anti-gay prejudice is not enough to justify discrimination in the political process.''

``This makes the Constitution real for lesbians and gay men,'' said Matt Coles of the American Civil Liberties Union's lesbian and gay rights project.

However, Gary Bauer, president of the conservative Family Research Council which supported Colorado's effort to reinstate the amendment, said, ``It's a very dark day for the liberty rights of the American people.''

``The judges seem to be saying that there are some matters so important that we will not allow the American people to decide them,'' Bauer said.

The Rev. Lou Sheldon of the Traditional Values Coalition said, ``Homosexuals are not an aggrieved minority, and disapproval of their choice of a deviant lifestyle is not the equivalent of bigotry or prejudice'' based on race or sex.