While there have been reports of unnamed sources witnessing the two alone together in the White House, Lewis Fox is the first to come forward and make the claim in person. He spoke first to the Washington Post.
Mr Clinton has been engulfed in allegations that he had sexual relations with Ms Lewinsky, who is now 24, and that he told her to lie about them since the scandal first broke on 21 January.
The assertions of Mr Fox, who retired early last year, could be important because the President is widely believed to have stated in a deposition he gave in the parallel Paula Jones sexual harassment case that he had never spent time alone with Ms Lewinsky.
Hillary Clinton, meanwhile, made a fresh attempt yesterday to blunt the scandal. Talking to reporters, she suggested that the entire imbroglio would eventually start to fade. "I don't anticipate that this will evaporate. But I anticipate it will slowly dissipate over time under the weight of its own insubstantiality," she said.
An appearance by Ms Lewinsky in front of the grand jury empanelled by the special prosecutor, Kenneth Starr, which had been set for today has been postponed at least until next Tuesday. There was speculation that a deal could be struck before then between Mr Starr and Ms Lewinsky's lawyers that would give her immunity from criminal prosecution.
Ms Lewinsky's mother, however, Marcia Lewis, began a second day of testimony before the grand jury in Washington yesterday. Daughter and mother lived together at the Watergate apartment complex in Washington at the time that the alleged liaisons with the President took place.
In his remarks, Mr Fox said he remembered Ms Lewinsky arriving at the White House one weekend day in late 1995 with an armful of official papers and asking to see the President. He said that he showed her in and that they were alone together. He had not seen her leave when he left his post after 40 minutes.
Mrs Clinton refused to address Mr Fox's claims. James Carville, an old trouble-shooting supporter of the President, told one interviewer: "Why would the Washington Post report that, when they know full well that there are four doors into the Oval office? Why didn't they choose to report that anyone can walk in any door, none of them are locked?"Reuse content