A veteran Defense Department investigator says he is facing a recommended 30-day suspension without pay for asking "inappropriate" questions during a background investigation of former senator Gary Hart, who had been nominated for a sensitive Pentagon advisory post by Defense Secretary William S. Cohen.

"With the work we do, people are not always happy with us," said David Kerno, a 19-year veteran with the Defense Security Service who is based in Lakewood, Colo. "But I've never had it come back at me this hard before."

Within hours after Kerno asked Hart's Denver law partners about the sex life of the former senator, whose 1988 presidential bid derailed over allegations of infidelity, Hart was on the telephone complaining to Cohen, a friend from the days when both were in the Senate.

Two days later, the Defense Department pulled Kerno off the Hart investigation. Kerno also lost his badge and his government car and was reassigned to a desk job. Kerno and his supporters claim his problems are having a chilling effect on other background investigators.

"The feeling among investigators is, if they have a high-profile case, they are not going to push it or they will end up like Dave," said Scott Evans, a Denver lawyer and a former investigator who is a friend of Kerno's. "If a public figure disapproves of what you are doing, you will be hung out to dry."

Pentagon officials say the incident simply involves one agent who may have gone too far. "These questions are not routinely asked" in a background check, said spokesman Kenneth Bacon.

On a flight back from a week-long trip to visit NATO allies in Europe, Cohen told reporters he did not speak with Hart about Kerno and did not influence Kerno's disciplinary process, which was first reported in USA Today.

"I was aware that [Hart] had complaints," Cohen said. "Frankly, I did not get involved and did not follow the situation. I took no action, nor did I ask anyone else to take any action on it."

Cohen said he remains unsure precisely what questions Kerno asked. But Cohen said he could understand Hart's concerns that such intimate inquiries could discourage others from seeking a public appointment.

"Any time you have these background clearances," Cohen said, "they should be conducted with some measure of discretion so that people are not certainly insulted by questions that really seem inappropriate."

The dispute arose in September, shortly after Cohen named Hart to the National Security Study Group, which is reviewing U.S. defense needs.

The appointment required a top-secret security clearance. The security service assigned Kerno, 53, to do a routine check on the Colorado Democrat.

Kerno said federal regulations bar him from discussing what took place. But sources on all sides agree on the broad outlines.

Kerno visited Hart's Denver law firm and asked a series of standard questions. During interviews with Hart's secretary and two law partners, someone mentioned Hart's problems with Donna Rice, said Evans, who heard Kerno's version of events and is acting as his spokesman.

Kerno was well aware that a decade earlier the married Hart was caught spending the weekend with Rice, then a part-time model and aspiring actress. The discovery abruptly halted Hart's campaign for the presidency.

"My job is to determine whether someone is a risk, based on his lifestyle," Kerno said. "I operated within the scope of DOD regulations. There is no doubt about that."

So Kerno asked whether Hart's colleagues knew of any extramarital affairs that might invite blackmail. "Those are areas we do investigate, because of the exposure for blackmail and coercion," Kerno said. Hart's colleagues stressed that they knew of nothing improper, Evans said.

Kerno described the brief interview sessions as low-key and professional. No one complained during the interviews, he said.

Hart declined to characterize Kerno's questions to a Post reporter, as did Hart's secretary. His two law partners did not return phone messages.

But Bacon said people at the law firm believed that the questions crossed a line. Investigators need to use discretion and consider an appointee's reputation and record when choosing questions, Bacon said. He described Hart as a "known quantity" who had handled sensitive material in the past.

Shortly after Kerno left the law firm, Hart telephoned Cohen's office and complained to chief of staff Robert Tyrer, Bacon said. Hart told Tyrer that if such questions were permitted, the Pentagon might have a hard time persuading people to volunteer for future panels, Bacon said.

When Kerno showed up for work two days later, he was given a new job: punching up criminal records on a computer.

A disciplinary report provided to Kerno said Hart voiced his displeasure directly to Cohen, but Bacon said that was an error. Cohen and others familiar with the exchange said only Tyrer was involved. Tyrer did not return phone calls.

The security service later briefed Tyrer on its findings, Bacon said, but Tyrer did not ask that Kerno be disciplined.

The inquiry into Kerno's actions lasted 10 months, during which Hart won his clearance and became co-chairman of the defense panel. Investigators told Kerno that the service no longer looked into allegations of adultery, said Evans, who attended one session as Kerno's lawyer. Evans contended that such questions were routine in the past.

A few months before the Hart investigation, he said, Kerno had been removed from a supervisory position because of his complaints that the service had become too timid.

"All I want is my day in court," Kerno said. "I was doing the job that taxpayers pay me to do. I'm not going to roll over for the DOD--or anybody."