ASHINGTON, Dec. 10 - The Supreme Court accepted an appeal on Friday from still another Texas death-row inmate in a case with significant international implications. The question is whether the federal government can permit Texas to execute a Mexican whose rights under a binding international treaty were violated when he was tried and sentenced to death without Mexican officials being notified.

On March 31, the International Court of Justice ordered the United States to undertake "an effective review" of the convictions and sentences of the inmate, José Ernesto Medellín, and 50 other Mexicans under death sentences in nine states. The court, usually known as the World Court, ruled that all 51 had been deprived of their right under the Vienna Convention on Consular Relations to meet with Mexican government representatives.

Mr. Medellín's lawyers raised this issue on his behalf as early as his appeal in the Texas state courts in 1998. But that was not early enough, the United States Court of Appeals for the Fifth Circuit ruled in May when it responded to the World Court decision by rejecting Mr. Medellín's request for a writ of habeas corpus. The appeals court ruled that he could obtain no relief on the basis of the consular treaty because, by failing to raise it at his murder trial in 1994 he was procedurally barred from raising it in federal court.

At his 1994 trial for a gang-related murder, Mr. Medellín, an indigent 18-year-old, was given a court-appointed lawyer who called no witnesses. Unknown to the trial judge at the time, Mr. Medellín's lawyer had been suspended from law practice for ethical violations. At the penalty phase of the trial, which lasted two hours, the lawyer put on only one expert witness, a psychologist who had never met Mr. Medellín.

The Vienna Convention, which the United States ratified in 1969, requires the authorities of a government that is detaining a foreign citizen to act "without delay" in notifying the prisoner of the right to request help from a consul of his home country. Mexican officials learned that Mr. Medellín had been convicted of murder after he had been on death row for three years. Mexico sued the United States in the World Court last year on behalf of Mr. Medellín and the other Mexican inmates.

The Supreme Court decision to accept Mr. Medellín's appeal was notable because the court neither received nor invited the views of the Bush administration before it acted. The case, Medellín v. Dretke, No. 04-5928, will be argued in March. The United States opposed Mexico's suit in the World Court, describing it in a brief as "an unjustified, unwise and ultimately unacceptable intrusion in the United States criminal justice system."

In its ruling, the World Court denied the request to nullify the Mexicans' convictions. Instead, it ordered the United States to provide an "effective review" of each case.

At the time of the ruling, the execution of Osbaldo Torres, a Mexican on Oklahoma's death row, was imminent, scheduled for May 18. The Oklahoma Court of Appeals responded to the decision by delaying the execution, and Oklahoma's governor, Brad Henry, then commuted the sentence to life in prison.

Mr. Medellín has encountered a different response. Texas filed a brief opposing a Supreme Court review of his case, arguing he has already received the "full merits review" of his case to which the World Court found him entitled.

The specific legal issue in the appeal is whether the Fifth Circuit was correct in applying to a case based on international law the usual procedural rules under which a defendant forfeits a claim that is not raised at the proper stage.

In a brief, unsigned order in a 1998 case that involved a Paraguayan inmate who tried to assert his rights under the Vienna Convention, the Supreme Court suggested that the treaty was subject to each country's procedural rules.

The Fifth Circuit, in its ruling in Mr. Medellín's case, said it was barred by the Supreme Court case from considering his petition.

But "the legal universe has fundamentally changed" since 1998, Mr. Medellín's lawyers said in their Supreme Court appeal, noting that the World Court interpreted the treaty in a 2001 case and again in the decision in March to create enforceable individual rights.

In their Supreme Court appeal, the lawyers sought to underscore the importance of the issue by presenting "friend of the court" briefs from international law scholars, former diplomats, international human rights organizations, the European Union and the Mexican government.

While these briefs undoubtedly attracted the court's attention, the justices have also demonstrated growing concern over the administration of the death penalty in Texas and the reviews that the Fifth Circuit gives to appeals from its death row.

On Monday, the court took the unusual step of hearing a second appeal from a Texas prisoner, Thomas Miller-El. The issue was whether the Fifth Circuit, which had rejected his challenge to the exclusion of blacks from the jury at his murder trial, had followed the Supreme Court's previous instructions to reconsider his challenge to how the prosecution questioned and eliminated potential jurors.