The Defense Department has dropped plans to suspend a veteran investigator for asking "inappropriate" questions about the sex life of former senator Gary Hart, who had been nominated for a sensitive Pentagon post by Defense Secretary William S. Cohen.

David Kerno, a 19-year veteran with the Defense Security Service, said he was handed a one-sentence letter on Friday that said the disciplinary action had been withdrawn. Kerno was reinstated as an investigator but received no explanation or apology, said his lawyer, Daniel Minahan.

"We're happy, but it's not all better," Minahan said. "He had a good chunk of his career stained."

A Defense Department spokesman would not say what led to the department's decision, which had been widely criticized by Republicans in Congress.

"The bottom line is, nothing will happen to Dave Kerno," said the spokesman, Glenn Flood. "We pulled it back; we're not going to do anything."

Flood denied charges that Kerno had been targeted because Hart and Cohen are longtime friends. He said he could not respond to Minahan's allegations that the suspension was dropped only after House Republicans lodged a written complaint.

Kerno's troubles began in September, shortly after Cohen named Hart to the National Security Study Group, which is reviewing U.S. defense needs. Hart, a Colorado Democrat, needed a top-secret security clearance for the position, and Kerno was assigned to do a routine background check.

During the inquiry, Kerno asked Hart's partners at a Denver law firm about the sex life of the former senator, whose 1988 presidential bid derailed over allegations of infidelity. Within hours, Hart was on the telephone complaining to Cohen's office.

Cohen later said he knew of the call but did not intervene in the case. Yet, within two days of Hart's call, the Defense Department pulled Kerno off the investigation. He lost his badge and was reassigned to a desk job.

Kerno's supervisors later recommended that he face a 30-day suspension without pay. His supporters charged that the action had a chilling effect on other background investigators and created morale problems within the service.

Kerno explained in a July interview that extramarital affairs are considered potential security problems because they can lead to blackmail.

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

Even so, a Pentagon spokesman said last month, people at the law firm believed Kerno's questions crossed a line. Investigators need to use discretion and consider an appointee's reputation and record when choosing questions, spokesman Kenneth Bacon said at the time. He described Hart as a "known quantity" who had handled sensitive material in the past.

Minahan said he might ask the Pentagon to compensate Kerno for the damage the investigation has caused to his reputation.

"He's got a long history and a clean record," Minahan said. "Whatever he did, I can't understand why it could not have been dealt with in a less drastic manner."