Nearly all prospective federal prosecutors are being asked if they are homosexual under a new Justice Department policy that officials say is aimed at gauging their vulnerability to blackmail.

The inquiry is part of a standard questionnaire, put into effect last year, that examines such personal subjects as whether the applicant has used illegal drugs, had problems with alcohol or failed to file income tax returns. All U.S. attorneys must certify that those hired as prosecutors have been asked these questions.

As part of the inquiry, if an applicant for an assistant U.S. attorney's job admits that he is homosexual, he is then asked whether his friends and family know about it.

"This is a question that is directly related to the sensitivity of the position," Justice Department spokesman Patrick Korten said. "It is not, repeat not, a bar to employment." He added, however, that if an applicant makes a secret of his homosexuality, that would be "an important consideration" in a decision not to hire him.

"It is, potentially at least, a matter of possible blackmail," Korten said. "In a sensitive position like this, where you are handling spy cases or criminal cases, you cannot afford to have someone on the staff who for any reason might be susceptible to blackmail."

Korten said the department is aware of no blackmail attempt involving a homosexual prosecutor in recent years. A number of recent corruption cases have involved prosecutors who accepted bribes or became dependent on drugs.

Jeff Levi, political director of the National Gay and Lesbian Task Force, called the questioning "a not very subtle attempt to identify gay employes." He said he is concerned that the inquiries are being used to discriminate against homosexuals, saying that Attorney General Edwin Meese III "has never been sympathetic to gay people."

"The blackmail notion is one we thought we had debunked a long time ago," Levi said. "Gay people are no more subject to blackmail than heterosexuals. If they are seriously concerned about secret sexual activity, they should be asking married heterosexuals if they're cheating on their wives."

Korten said that heterosexual applicants would be rejected only if "their sexual lifestyle was notorious" and "disruptive."

"There are several assistant U.S. attorneys around the country who are homosexual, and we have no problem with that as long as it is known; as long as they are out of the closet, in the current lexicon," Korten said.

The questionnaire was drawn up by an advisory committee because background checks were turning up drug use or other personal problems by prosecutors who had already been hired on a temporary basis, Korten said. "The purpose of sending out this questionnaire was to get U.S. attorneys to ask these questions up front," he said.

Homosexuality was "a serious obstacle" to federal employment until the early 1970s, when government policy changed after a threatened lawsuit, Korten said. But he said all federal intelligence agencies still ask applicants for sensitive jobs whether they are homosexual because of blackmail concerns.

A spokesman for the Office of Personnel Management said there is no government-wide policy on the subject.