NEWARK, N.J. (AP) _ Federal authorities are investigating whether a man traveling with Gary Hart falsely identified himself as a Secret Service agent and ordered passengers bumped from a flight the candidate was taking.

The allegation has ''enough credibility to investigate it,'' said Jane Vezeris, a Secret Service spokeswoman. She refused further comment, saying the agency does not release details of its inquiries.

A Precision Eastern Express Airlines agent at Newark International Airport reported being approached by Hart and three others, one of whom said, ''I'm with the Secret Service and no one else can board this flight except Mr. Hart and his party,'' according to airline spokesman Fred Martin.

The man showed identification that included a badge, and the airline agent bumped seven people who had reservations on the 15-seat plane that was taking Hart to New Hampshire on Wednesday, said Martin, vice president of marketing for the Manchester, N.H., carrier.

The passengers ''were extremely upset,'' and were put on another flight about 30 minutes later, he said.

Hart has no Secret Service agents assigned to travel with him, aides to the former Colorado senator said.

Hart, who had reservations on the flight, was escorted in a limousine to the plane on the tarmac by airport police, Martin said.

Ginny Terzano, a press aide for the Hart campaign in Denver, said she could not confirm any details of the incident, but suggested the man involved may have been a security agent from a private firm.

''What we think happened is that a Pinkerton agent went up to a gate agent for Eastern Express and said he was a security agent and to get things moving,'' said Ms. Terzano.

''The security agent was not a Hart staffer or a Hart aide. That person had nothing to do with the Hart campaign,'' she said.

However, Pinkerton headquarters in New York denied that one of its agents was reponsible.

''We confirm that we provided two security professionals to the Gary Hart campaign in New York on May 6,'' the company said. ''One of these individuals accompanied Mr. Hart to Newark Airport, where his assignment ended. The security professional did not have any contact with airline or airport personnel concerning flight or baggage arrangements for Mr. Hart or his staff. Further, he did not represent himself to be a Secret Service official at any time.''

In Littleton, N.H., Wednesday evening, Hart's press secretary Kevin Sweeney said he and two other aides traveled with the candidate from Newark, but that he knew nothing of the alleged incident except from reporters' questions.

Sweeney identified the other aides as Michael Stratton and Billy Shore.

Impersonating a Secret Service agent is a felony that can carry a $1,000 fine and a three-year prison sentence, Ms. Vezeris said.

Precision Eastern Express, a subsidiary of Eastern Airlines, serves Vermont, New Hampshire, Massachusetts, New York, New Jersey and Pennsylvania.