federal judge in New York declared the death penalty unconstitutional today, saying evidence has shown that there is an "undue risk" that a meaningful number of innocent people have been executed.

The ruling by Judge Jed S. Rakoff is the first to declare the current federal death penalty unconstitutional. The judge's ruling will have no immediate impact in New York or across the country unless it is upheld on the appellate level. But it is certain to become part of the debate over capital punishment.

The decision came in the case of two men — Alan Quiñones and Diego Rodriguez — who are facing trial on narcotics and murder charges and whose lawyers had argued in pretrial motions that the death penalty was unconstitutional.

Judge Rakoff, who sits on the Federal District Court in Manhattan, had told lawyers in the case in a preliminary ruling in April that he intended to declare the death penalty act unconstitutional unless prosecutors could persuade him otherwise. Today, he followed through on that earlier thought.

"In brief, the court found that the best available evidence indicates that, on the one hand, innocent people are sentenced to death with materially greater frequency than was previously supposed and that, on the other hand, convincing proof of their innocence often does not emerge until long after their convictions," Judge Rakoff wrote in his 28-page opinion.

"It follows," he continued, "that implementation of the Federal Death Penalty Act not only deprives innocent people of a significant opportunity to prove their innocence, and thereby violates procedural due process, but also creates an undue risk of executing innocent people, and thereby violates substantive due process."

The United States attorney's office issued a terse statement this afternoon in response to the ruling.

"As we set forth in our submissions to the court in this matter, the Federal Death Penalty Act is constitutional," said United States Attorney James B. Comey. "In light of Judge Rakoff's decision, we are considering our appellate options."

Judge Rakoff, who issued his preliminary ruling on April 25, said he based his finding in part on academic research about death row inmates who had been wrongfully convicted. He also cited cases in which death row inmates had been exonerated through DNA and other evidence.

"By cutting off the opportunity for exoneration," Judge Rakoff wrote, the federal death penalty "denies due process and, indeed, is tantamount to foreseeable, state-sponsored murder of innocent human beings."

Mr. Quiñones and Mr. Rodriguez are scheduled to go on trial in September in connection with a drug-related killing in the Bronx three years ago. They are accused of torturing and killing an informer, Edwin Santiago, on June 27, 1999. The United States attorney in Manhattan at the time, Mary Jo White, had declined to seek the death penalty, but was overruled by Attorney General John Ashcroft, prompting defense lawyers to challenge the constitutionality of the Federal Death Penalty Act.

Prosecutors had argued that it was premature for Judge Rakoff to decide the constitutionality of the death penalty because the trial had not yet occurred, and the men had not been convicted or sentenced to death.

But Judge Rakoff disagreed, saying that the government's decision to seek the death penalty will have a significant impact on how the jury is selected, and thus on the trial itself. "In short," the judge said, the issue is not only "ripe for adjudication at this time, it cannot be postponed without material prejudice to the defendants."

Even before his final ruling today, Judge Rakoff's position on the issue had set off a debate between prosecutors and scientists.

In arguing against the judge's preliminary position, prosecutors had said that the studies Judge Rakoff cited had "serious methodological flaws."

That brought a response from the scientific community, with 42 criminologists, sociologists and psychologists submitting a "friend of the court" brief in which they attacked the prosecution's argument as inaccurate and unfair.

In his ruling, Judge Rakoff noted that since 1993 at least 12 death row inmates have been exonerated through DNA testing. In each case, the defendant had been found guilty by a unanimous jury that concluded there was proof of his guilt beyond a reasonable doubt, and convictions in each of the 12 cases were affirmed on appeal.

The government argued that DNA testing is now available before a trial in many cases and will actually help reduce the risk of mistaken convictions.

"This completely misses the point," Judge Rakoff responded. "What DNA testing has proved, beyond cavil, is the remarkable degree of fallibility in the basis fact-finding processes on which we rely in criminal cases."

The United States Supreme Court banned capital punishment in 1972, but the death penalty was reinstated in 1976. New York is one of 38 states that has the death penalty.

Judge Rakoff, 58, a graduate of Harvard Law School and a former federal prosecutor, was nominated by President Bill Clinton on Oct. 11, 1995, for a seat on the Federal District Court for the Southern District of New York and he was confirmed by the Senate two months later. He joined the court in January 1996.

Judge Rakoff has attracted considerable attention from the news media well before today.

Last week he was named to oversee the Securities and Exchange Commission's lawsuit charging WorldCom with accounting fraud. He has also become involved in the case of an innocent Egyptian student who was detained in connection with the attack on the World Trade Center. It was reported last week that Judge Rakoff was considering opening an inquiry into how the F.B.I. got what turned out to be a false confession from the student, who spent a month in jail before authorities released him, saying that he was not guilty of any involvement in the attack.

In September of last year, Judge Rakoff became embroiled in an ethics debate, when he refused to recuse himself from a lawsuit against Texaco Inc. brought by a group of Ecuadorean Indians who accused the oil company of polluting their land in the Amazon rain forest. Lawyers for the Indians said Judge Rakoff had attended an expenses-paid seminar in 1998 in Montana at which a former chairman of Texaco spoke. They argued that this created the appearance of a conflict of interest.

Judge Rakoff confirmed that he had attended the seminar, but he said the lawsuit was never discussed.