On the advice of her lawyer, 29-year-old Jan Tyler is refusing to talk with either the FBI or reporters.

But she is the "missing" witness everyone wants to interview.

The blond Tyler, who has gone into seclusion, has been identified as being with White House Chief of Staff Hamilton Jordan at Studio 54 in New York on the night of June 27, 1978 -- the evening when he is accused of allegedly sniffing cocaine.

Tyler, whose job resume lists her as having been "administrative assistant" to Jordan, went to work at Penthouse magazine in New York on July 11, 1977. She got the job as the result of a hand-written letter of recommendation from Jordan.

At Penthouse, Tyler was in charge of "Pet Promotion." The magazine's "Pets" are their nude models. It was Tyler's job, according to a Penthouse source yesterday, to line up appearances "at auto shows, opening car doors, or refrigerator doors at home shows, or anyplace else where someone promoting something wanted to Rent-A-Bunny."

Tyler left Penthouse on June 30, 1978, three days after the incident at Studio 54, Elkin Abramowitz, the attorney representing her in New York, said this week that he has advised her to disappear for the time being. She will not be talking to reporters, he said, nor has she yet agreed to talk with anyone from the Justice Department.

Tyler, her lawyer said, has a "similar problem" to another accuser of Jordan's in California who at first demanded immunity before she would talk to FBI agents.

Tyler has been identified to The Washington Post as having been with Jordan, in a party that included two other men and two other women.

A Fugazy limousine chauffeur who drove the party, first to dinner at "21" and then to Studio 54, described Tyler as "a very classy lady . . . you could tell she had gone to college and was a career girl."

The two other women, whose names he did not know, did not appear to him to "be in the same league."

Tyler, who is from Atlanta, worked for Jordan on the presidential campaign. She is a graduate of the University of Georgia, according to her personnel records.

It was she, according to the chauffeur, who took Jordan's party to Studio 54, getting out of the car to persuade the doorman that they were important enough to be granted admittance.

She was present with Jordan during the time he is alleged to have smiffed cocaine. Her version of what happened that night is crucial to anyone hoping to get at the truth; But so far, she is saying nothing, publicly or privately . . .

The bankrupt closing of Doctor's Hospital has caused the worry lines to deepen in a lot of Washington's more famous faces. Not because they had money invested, but because they were scheduled in coming months for cosmetic touch-ups by one of the city's most popular plastic surgeons. Dr. Clyde Litton. He had his own operating room there for his exclusive use, sources close to him say, and now is going to have to look elsewhere in a city already overbooked for more serious surgery . . .

If Sen. Frank Church were a Republican, his candidate for the presidency would be Sen. Howard Baker of Tennessee. Church paid tribute to his colleague across the aisle at a dinner the other night, saying Baker probably wouldn't get the nomination, but is, nevertheless, the "ablest" contender . . .

They didn't even announce it in the Boston papers, but novelist George Higgins ("The Friends of Eddie Coyle:) and longtime Kennedy loyalist Loretta Cubberley were married last month. Loretta, now an executive for Polaroid; worked on Sen. Edward M. Kennedy's staff, where she is best remembered for labeling the male chauvinist hiring practices on Capitol Hill as the "Alger Hiss Principle,": "Any girl too young ever to have heard of Alger Hiss and too dumb to know who he is otherwise has a better chance of getting hired than a girl old enough and/or smart enough" . . .

The bottom has dropped out of the market for Washington roman a clef novels. Writers who once could expect six-figure offers from publishers for anything they could envision with a Capitol dome or a White House view on the book jacket are now busily spinning the globe, looking for new locales. Les Whitten's new work-in-progress has been shifted to Philadelphia. Warren Adler is researching Egypt and columnist William Safire is even reaching backward in time to place his characters in a historical setting . . .

Alejandro Orfila, certain to be re-elected this month to the post of secretary-general of the Organization of American States, takes the "general" part of his title ver seriously. Since he took over, guards at the Pan American Union have been taught military spit-and-polish and are required to snap to attention and salute when their commander-in-chief enters or leaves the building . . ;

She may not be sewing the American flag, but Rosalynn Carter has a sewing machine on the second floor of the White House. There, she can "hem Amy's jeans, let out seams and sew up rips and tears," an aide says.