One of America’s top judges said in an interview broadcast in Britain yesterday that interrogators can inflict pain to obtain critical information about an imminent terrorist threat.

Justice Scalia said aggressive interrogation could be appropriate to learn where a bomb was hidden shortly before it was set to explode or to discover the plans or whereabouts of a terrorist group.

“It seems to me you have to say, as unlikely as that is, it would be absurd to say you couldn’t, I don’t know, stick something under the fingernail, smack him in the face. It would be absurd to say you couldn’t do that,” Justice Scalia told British Broadcasting Radio Corp.

Justice Scalia said determining when physical coercion could come into play was a difficult question. “How close does the threat have to be? And how severe can the infliction of pain be? I don’t think these are easy questions at all, in either direction,” he told the BBC’s “Law in Action” program.

American interrogation techniques, including waterboarding, have been the subject of growing debate in America, and could play a role in the military trials of six men charged in connection with the September 11, 2001, attacks.

The issue also could find its way to the Supreme Court.

Justice Scalia, visiting London during a break in the court’s calendar, referred generally to those methods as “so-called torture,” and said practices prohibited by the Constitution in the context of the criminal justice system — including indefinite detention — are readily allowed in other situations, such as when a witness refuses to answer a question in court.

“I suppose it’s the same thing about so-called torture,” he said in the interview. “Is it really so easy to determine that smacking someone in the face to find out where he has hidden the bomb that is about to blow up Los Angeles is prohibited by the Constitution?

“Is it obvious, that what can’t be done for punishment can’t be done to exact information that is crucial to the society? I think it’s not at all an easy question, to tell you the truth.”

Justice Scalia, a judicial icon among American conservatives, an acerbic wit and often-abrasive personality, said Europeans had no business “smugly” decrying those techniques as torture. Earlier in the interview he also faced down criticism of the death penalty in America.

“Europeans get really quite self-righteous, you know, [saying,] ‘no civilized society uses it.’ They used it themselves — 30 years ago,” he said, adding that a majority of Europeans probably supported capital punishment anyway.