The United States signed the Vienna Convention treaty in 1963, in part to protect the rights of American citizens who are arrested in other countries. The treaty requires foreign authorities to provide an accused citizen prompt access to U.S. officials.

But the provisions apply in the United States, too, and a Vietnamese man arrested in Fairfax County last year in connection with a double homicide could avoid the death penalty if convicted, because his rights under the Vienna Convention apparently were violated.

As the immigrant population in the Washington area swells, the case of Dinh Pham serves as a reminder to police officers of an additional duty when they arrest foreign nationals: to inform them, without delay, that they have a right to consult with their embassy or consulate.

The issue has been argued before the International Court of Justice, and the U.S. Supreme Court recently considered the case after the international court found last year that 51 Mexicans were convicted without being told of their right to consular advice.

President Bush ordered Texas officials to review all of those cases.

And based on the international court's ruling and advice from the State Department, the governor of Oklahoma last year commuted the death sentence of a Mexican man convicted of a double murder because he had not been advised of his Vienna Convention rights.

Pham's case has not gone to trial, and there is no precedent for what remedy might be appropriate if his Vienna Convention rights were violated.

His attorneys are proposing that Fairfax Circuit Court Judge Leslie M. Alden throw out the possibility of capital punishment for Pham, who is accused of strangling a Merrifield woman and her 22-month-old daughter in their home in January 2004.

The day after the bodies of Loan Phuong Nguyen, 30, and her daughter, Ashley Nu Ton, were discovered, Pham was stopped while driving Nguyen's vehicle. Through a Vietnamese interpreter, he admitted the killings to Fairfax homicide detectives in a taped statement and was arrested and charged with murder.

A transcript of the interview shows, and Fairfax prosecutors do not contest, that the detectives did not advise Pham that he had a right to speak with the Vietnamese Embassy.

Two weeks after Pham's arrest, the detective faxed a notice to the Vietnamese Embassy that Pham was in custody.

The Vienna Convention states that if a foreign national is arrested in this country, "authorities shall inform the person concerned without delay of his rights" to speak with someone from his embassy or consulate. The State Department's guide to local law enforcement advises officers that "you should treat a foreign national as you would want an American citizen to be treated in a similar situation in a foreign country. This means prompt, courteous notification to the foreign national of the possibility of consular assistance."

Paul A. Maslakowski, the acting capital public defender representing Pham, said that if Pham had known of his rights, "he certainly would have requested contact and would have refrained from speaking to the police until he had obtained the advice of consular officials."

Maslakowski suggested that the judge throw out the death penalty as a deterrent to other police agencies.

Fairfax prosecutors responded that the failure to notify Pham of his rights did not prejudice his case and that if the judge eliminated the possibility of the death penalty, she "would in essence be stepping into the roles of prosecutor and legislator," Deputy Commonwealth's Attorney Raymond F. Morrogh wrote.

Fairfax police have a written policy of informing arrested foreign nationals of their right to contact their embassy or consulate, though it apparently was not followed in Pham's case.

Practices in other jurisdictions vary. Prince William County police carry a two-sided card with instructions on how to inform foreign nationals of their rights. District police notify only the person's embassy, not the suspect himself, Sgt. Joe Gentile, a police spokesman, said.

Alexandria police have no policy on foreign nationals, spokeswoman Amy Bertsch said.