WASHINGTON — The U.S. Supreme Court (search) rejected Texas' gay sex ban Thursday, ruling that a state law that punished homosexual couples for engaging in sex acts that are legal for heterosexuals was an unconstitutional violation of privacy.

The justices struck down a Texas Supreme Court (search) ruling that banned "deviate sexual intercourse with another individual of the same sex."

• Raw Data: Lawrence v. Texas (PDF)

The case was brought by two men who were caught by police engaging in an illegal sex act at home.

The law "demeans the lives of homosexual persons," Justice Anthony M. Kennedy (search) wrote for the 6-3 majority, adding that the men "are entitled to respect for their private lives." 

"The state cannot demean their existence or control their destiny by making their private sexual conduct a crime," Kennedy wrote.

Justices John Paul Stevens, David Souter, Ruth Bader Ginsburg and Stephen Breyer agreed with Kennedy in full. Justice Sandra Day O'Connor agreed with the outcome of the case, but not all of Kennedy's rationale.

Chief Justice William H. Rehnquist and Justices Antonin Scalia and Clarence Thomas dissented.

"The court has largely signed on to the so-called homosexual agenda," Scalia wrote for the three. He took the unusual step of reading his dissent from the bench.

"The court has taken sides in the culture war," Scalia said, adding that he has "nothing against homosexuals."

Texas officials had defended the law before the court, saying it promoted the institutions of marriage and family, and arguing that communities have the right to choose their own standards.

Ken Connor, president of the Family Research Council (search), decried the court's decision, saying it will help "overturn" and "deconstruct" the idea of traditional marriage.

"The institution of families has lost," Connor told Fox News, pointing out that gay sex leads to a significant number of sexually transmitted disease cases.

But Michael Adams, director of education and public affairs at the Lambda Legal Defense and Education Fund (search), hailed the ruling as a victory for gay rights.

"This is not an issue about sexually transmitted diseases, this is about what kind of country we're going to have," he told Fox News. "Our right to privacy and our right to equal treatment needs to be respected like everybody else's."

Professor Paul Rothstein, a constitutional law professor at Georgetown University, said the justices did not strike down the Texas law because it treated gays differently from heterosexuals, but rather because of how much it violated people's privacy.

"These are acts, these sodomy acts, that both heterosexuals and homosexuals engage in," Rothstein said.

"[The justices] chose much broader ground. There are certain things you do in the privacy in your home between consenting adults … that grants a very broad right to people and prevents the states from infringing on it."

The court's decision reversed course from a ruling 17 years ago that states could punish homosexuals for what such laws historically called deviant sex.

The case was a major re-examination of the rights and acceptance of gay people in the United States. More broadly, it also tested a state's ability to classify as a crime what goes on behind the closed bedroom doors of consenting adults.

Laws forbidding homosexual sex, once universal, now are rare. Those on the books are rarely enforced but underpin other kinds of discrimination, lawyers for the two Texas men had argued to the court.

The two men at the heart of the case, John Geddes Lawrence and Tyron Garner, have retreated from public view. They were each fined $200 and spent a night in jail for the misdemeanor sex charge in 1998.

The case began when a neighbor with a grudge faked a distress call to police, telling them that a man was "going crazy" in Lawrence's apartment. Police went to the apartment, pushed open the door and found the two men having anal sex.

As recently as 1960, every state had an anti-sodomy law. In 37 states, the statutes have been repealed by lawmakers or blocked by state courts.

Of the 13 states with sodomy laws, four -- Texas, Kansas, Oklahoma and Missouri -- prohibit oral and anal sex between same-sex couples. The other nine ban consensual sodomy for everyone: Alabama, Florida, Idaho, Louisiana, Mississippi, North Carolina, South Carolina, Utah and Virginia.

Thursday's ruling apparently invalidates those laws as well.

The Supreme Court was widely criticized 17 years ago when it upheld an antisodomy law similar to Texas'. The ruling became a rallying point for gay activists.

Of the nine justices who ruled on the 1986 case, only three remain on the court. Rehnquist was in the majority in that case -- Bowers v. Hardwick -- as was O'Connor. Stevens dissented.

A long list of legal and medical groups joined gay rights and human rights supporters in backing the Texas men. Many friend-of-the-court briefs argued that times have changed since 1986, and that the court should catch up.

At the time of the court's earlier ruling, 24 states criminalized such behavior. States that have since repealed the laws include Georgia, where the 1986 case arose.

Texas defended its sodomy law as in keeping with the state's interest in protecting marriage and child-rearing. Homosexual sodomy, the state argued in legal papers, "has nothing to do with marriage or conception or parenthood and it is not on a par with these sacred choices."

The state had urged the court to draw a constitutional line "at the threshold of the marital bedroom."

Although Texas itself did not make the argument, some of the state's supporters told the justices in friend-of-the-court filings that invalidating sodomy laws could take the court down the path of allowing same-sex marriage.

The case is Lawrence v. Texas, 02-102.

The Associated Press contributed to this report.