By LINDA GREENHOUSE
 
WASHINGTON, Jan. 12 - The Supreme Court ruled on Wednesday that federal law prohibits the open-ended detention of Cubans who entered the United States during the Mariel boatlift in 1980 and who, despite crimes later committed in the United States, cannot be deported because the Cuban government refuses to take them back.

Voting 7 to 2, the court applied to the deportable group of Mariel Cubans the same rights it found in federal law in a decision four years ago that barred the indefinite detention of a stateless immigrant, lawfully admitted to the United States, whose criminal record made him deportable but who had no place to go.

The Bush administration had argued that the decision in the earlier case did not apply to the Mariel group because, unlike the immigrant, Kestutis Zadvydas, admitted as a refugee from post-World War II Europe, the Cubans had never been granted formal admission to the United States. Instead, they received a humanitarian parole, which the administration said did not entitle them to the same protection when they violated the country's hospitality by committing crimes.

But writing for the majority on Wednesday, Justice Antonin Scalia said that because the immigration statute itself made no such distinction, the court could not create one.

In Zadvydas v. Davis, the court held that because detention longer than six months could raise serious constitutional problems, the statute should be interpreted to avoid those problems by limiting detention of a deportable alien who did not pose a risk to the community. Justice Scalia said the fact that immigrants who had never been formally admitted into the country might have a more tenuous constitutional claim did not change the analysis.

Addressing the government's argument, Justice Scalia said: "If we were, as the government seems to believe, free to 'interpret' statutes as becoming inoperative when they 'approach constitutional limits,' we would be able to spare ourselves the necessity of ever finding a statute unconstitutional as applied."

The decision, Clark v. Martinez. No. 03-878, applied to two cases of Cubans found deportable. One, Sergio Suarez Martinez, convicted of burglary, theft and assault, was taken into custody by immigration officials and ordered removed from the country in January 2001. Eighteen months later, he filed a habeas corpus petition based on the Zadvydas decision, which was granted by a federal district court in Oregon in a decision that the United States Court of Appeals for the Ninth Circuit, in San Francisco, affirmed. Another federal appeals court, in Atlanta, reached the opposite conclusion in denying release to Daniel Benitez, who had filed a habeas corpus petition six months after he was detained and ordered deported for convictions for assault and gun possession.

Some 125,000 Cubans entered the country during the Mariel incident. The ruling on Wednesday will apply to as many as 1,000 who have been convicted of crimes and are being held without a realistic prospect of repatriation.

The administration had also argued that a decision in the Cubans' favor would raise national security concerns by making it more difficult to control the country's borders. "If that is so, Congress can attend to it," Justice Scalia said in his opinion.

The two dissenters were Justice Clarence Thomas and Chief Justice William H. Rehnquist, who said that the majority had mischaracterized the Zadvydas decision as applying to the Mariel group. Justice Thomas, in a part of his dissenting opinion that the chief justice did not join, said the Zadvydas decision should be overruled.

The case had drawn considerable attention from international and human rights groups. Deborah Pearlstein of the group Human Rights First, which had filed a brief, praised the court for rejecting "one of the farther reaching assertions of administrative power by the executive branch."

In another immigration decision on Wednesday, the court accepted the administration's argument that the absence of a functioning central government in Somalia did not prevent the deportation of Somalis to their home country.

A Somali man, Kayse G. Jama, who entered the United States as a 17-year-old refugee in 1996 and was later convicted of assault, argued that federal law required the consent of the receiving country before deportation. He lost his case in the United States Court of Appeals for the Eighth Circuit, in St. Louis, while the Ninth Circuit in a separate case had issued an injunction barring further deportations to Somalia.

The Supreme Court affirmed the Eighth Circuit's ruling by a 5-to-4 vote. Justice Scalia wrote the majority opinion in Jama v. Immigration and Customs Enforcement, No. 03-674. Justice David H. Souter wrote a dissenting opinion, joined by Justices John Paul Stevens, Ruth Bader Ginsburg and Stephen G. Breyer.

The dispute on the court was over statutory interpretation. The question was whether Congress, in a complex set of provisions dealing with deportation, meant to require the receiving country's consent as a condition of deportation for people in Mr. Jama's particular position. Some sections of the law include such a provision, and the majority said that the court should not find a "structural inference" that the requirement also applied to Mr. Jama's category.