ASHINGTON, June 26 — The Supreme Court issued a sweeping declaration of constitutional liberty for gay men and lesbians today, overruling a Texas sodomy law in the broadest possible terms and effectively apologizing for a contrary 1986 decision that the majority said "demeans the lives of homosexual persons." The vote was 6 to 3.

Gays are "entitled to respect for their private lives," Justice Anthony M. Kennedy said for the court. "The state cannot demean their existence or control their destiny by making their private sexual conduct a crime."

Justice Kennedy said further that "adults may choose to enter upon this relationship in the confines of their homes and their own private lives and still retain their dignity as free persons."

While the result had been widely anticipated since the court agreed in December to hear an appeal brought by two Houston men who were prosecuted for having sex in their home, few people on either side of the case expected a decision of such scope from a court that only 17 years ago, in Bowers v. Hardwick, had dismissed the same constitutional argument as "facetious." The court overturned that precedent today.

In a scathing dissent, Justice Antonin Scalia accused the court of having "taken sides in the culture war" and having "largely signed on to the so-called homosexual agenda." He said that the decision "effectively decrees the end of all morals legislation" and made same-sex marriage, which the majority opinion did not discuss, a logical if not inevitable next step. Chief Justice William H. Rehnquist and Justice Clarence Thomas signed Justice Scalia's dissent.

While some gay rights lawyers said that there were still abundant legal obstacles to establishing a right either to gay marriage or to military service by gay soldiers, there was no doubt that the decision had profound legal and political implications. A conservative Supreme Court has now identified the gay rights cause as a basic civil rights issue.

Ruth Harlow, legal director of the Lambda Legal Defense and Education Fund and the lead counsel for the two men, John G. Lawrence and Tyron Garner, called the decision "historic and transformative." Suzanne Goldberg, a professor at Rutgers Law School who had represented the men in the Texas courts, said that the decision would affect "every kind of case" involving gay people, including employment, child custody and visitation, and adoption.

"It removes the reflexive assumption of gay people's inferiority," Professor Goldberg said. "Bowers took away the humanity of gay people, and this decision gives it back."

The vote to overturn Bowers v. Hardwick was 5 to 4, with Justice Kennedy joined by Justices John Paul Stevens, David H. Souter, Ruth Bader Ginsburg and Stephen G. Breyer.

"Bowers was not correct when it was decided, and it is not correct today," Justice Kennedy said. "Its continuance as precedent demeans the lives of homosexual persons."

Justice Sandra Day O'Connor, who was part of the 5-to-4 majority in Bowers v. Hardwick, did not join Justice Kennedy in overruling it. But she provided the sixth vote for overturning the Texas sodomy law in a forcefully written separate opinion that attacked the law on equal protection grounds because it made "deviate sexual intercourse" — oral or anal sex — a crime only between same-sex couples and not for heterosexuals.

"A law branding one class of persons as criminal solely based on the state's moral disapproval of that class and the conduct association with that class runs contrary to the values of the Constitution and the Equal Protection Clause," Justice O'Connor said.

Texas was one of only four states — Kansas, Oklahoma and Missouri are the others — to apply a criminal sodomy law exclusively to same-sex partners. An additional nine states — Alabama, Florida, Idaho, Louisiana, Mississippi, North Carolina, South Carolina, Utah and Virginia — have criminal sodomy laws on their books that in theory, if not in practice, apply to opposite-sex couples as well. As a result of the majority's broad declaration today that the government cannot make this kind of private sexual choice a crime, all those laws are now invalid.

Twenty-five states had such laws at the time the court decided Bowers v. Hardwick. The Georgia sodomy law the court upheld in that case was overturned by a state court ruling in 1998. Some of the other state laws have been repealed and others invalidated by state courts.

In the Texas case, Mr. Lawrence and Mr. Garner were discovered by the Houston police while having sex in Mr. Lawrence's apartment. The police entered through an unlocked door after receiving a report from a neighbor of a "weapons disturbance" in the apartment. The neighbor was later convicted of filing a false report.

The men were held in jail overnight. They later pleaded no contest, preserving their right to appeal, and were each fined $200. The Texas state courts rejected their constitutional challenge to the law.

Asked today for the Bush administration's reaction to the ruling, Ari Fleischer, the White House press secretary, noted that the administration had not filed a brief in the case. "And now this is a state matter," he said. In fact, the decision today, Lawrence v. Texas, No. 02-102, took what had been a state-by-state matter and pronounced a binding national constitutional principle.

The delicacy of the moment for the White House was apparent. Groups representing the socially conservative side of the Republican Party reacted to the decision with alarm and fury. On the other hand, important libertarian groups had supported the challenge to the Texas law. Justice Thomas, who is often in sympathy with libertarian arguments, wrote a brief separate dissenting opinion today with a nod in that direction.

He said he would vote to repeal the law if he were a member of the Texas Legislature. "Punishing someone for expressing his sexual preference through noncommercial consensual conduct with another adult does not appear to be a worthy way to expend valuable law enforcement resources," Justice Thomas said, but added that he could not overturn the law as a judge because he did not see a constitutional basis for doing so.

Charles Francis, co-chairman of the Republican Unity Coalition, a group of gay and heterosexual Republicans seeking to defuse the issue within the party, said today, "I hope the giant middle of our party can look at this decision not as a threat but as a breakthrough for human understanding." The group includes prominent Republicans like former President Gerald R. Ford, David Rockefeller and Alan K. Simpson, the former senator from Wyoming, who is its honorary chairman. No member of the Bush administration has joined the group, Mr. Francis said.

As the court concluded its term today, the absence of any sign of a retirement meant that the issue was not likely to surface in judicial politics anytime soon. There was a tense and ultimately humorous moment in the courtroom this morning when, after the announcements of decisions, Chief Justice Rehnquist brought the term to a close with his customary words of thanks to the court staff.

"The court today notes the retirement," he then said drily as those in the audience caught their breath, "of librarian Shelley Dowling." A collective sigh and audible chuckles followed as the marshal, Pamela Talkin, banged her gavel and the nine justices left the bench, all of them evidently planning to return when the court meets on Sept. 8 for arguments in the campaign finance case.

Earlier, as Justice Kennedy was reading excerpts from his decision, the mood in the courtroom went from enormous tension and then — on the part of the numerous gay and lesbian lawyers seated in the bar section — to visible relief. By the time he referred to the dignity and respect to which he said gays were entitled, several were weeping, silently but openly.

The majority opinion was notable in many respects: its critical dissection of a recent precedent; its use of a decision by the European Court of Human Rights, supporting gay rights, to show that the court under Bowers v. Hardwick was out of step with other Western countries; and its many citations to the court's privacy precedents, including the abortion rights cases.

The citations to Roe v. Wade and Planned Parenthood v. Casey appeared particularly to inflame Justice Scalia. If Bowers v. Hardwick merited overruling, he said, so too did Roe v. Wade. He also said that laws against bigamy, adultery, prostitution, bestiality and obscenity were now susceptible to challenges.

The majority opinion did not precisely respond to that prediction, noting instead that the right claimed by Mr. Lawrence and Mr. Garner did not involve prostitution, public behavior, coercion or minors.

The fundamental debate on the court was over the meaning of the Constitution's due process guarantee, which Justice Kennedy said was sufficiently expansive so that "persons in every generation can invoke its principles in their own search for greater freedom."