When Officer Goodbody walked into Mayor Marion Barry's conference room last week, the mayor sat in front of about 100 of his closest friends and aides who had gathered to salute his 50th birthday.

The usually superconfident Barry was caught off guard when the "officer," clad in a policewoman's uniform, announced that he was under arrest. She handcuffed him, then flicked on her "boogie box" tape player and began to dance.

"I think he was speechless," recalled "Goodbody," whose real name is Catherine Langley.

Langley, a performer employed by the Eastern Onion Singing Telegrams service, was hired for $90 by an unidentified friend of the mayor's to take off her clothes. That meant, based on company policy, that she removed everything -- skirt, blouse, camisole and half-slip -- except her red bikini.

"It's a bikini. By definition it's small, but it covers all the parts that some might consider indecent if you expose them," she said in an interview.

"We're a class act," said Eastern Onion's manager, Myrna Orlov, who added that the person who had hired the firm asked to remain confidential.

Asked yesterday about the surprise performance, Barry said, "I didn't appreciate it or approve of it." He declined to say who had arranged it, but added that "the person who did it has been royally jacked up by me."

Patricia Seldon, the mayor's longtime executive assistant, confirmed that she had been tipped in advance to Langley's appearance. But she declined to reveal who hired Langley, except to say that it was a friend of Barry's "from outside government." Seldon added that the staff birthday party is an annual event.

It's also turning out to be an annual event for Langley, who was hired to perform as a belly dancer at last year's party.

"He really liked that," she recalled.

Langley said her act "is a strip tease -- things come off piecemeal, one at a time," but is not the "bump and grind routines" found in night clubs.

"It's a little bawdy. I do a lot of double entendres," she said, but "it's a clean, crisp jazzy dance set" interspersed with "a lot of patter."

"Oh, no, look what you made me do," Langley said she jokingly told the mayor at one point as she removed one of her garments.

Langley, who claims to have performed for U.S. senators, representatives and other power brokers -- "I've been all through the ritzy homes in Potomac, McLean and Northwest" -- said that Barry's reaction of embarrassment mixed with nervous laughter was typical.

Reaction from others at the party varied.

One Barry aide called it "tasteless," and "not the sort of thing we ought to be doing." But developer Jeffrey N. Cohen, a friend of the mayor's who attended the party, said that "a little harmless levity can always do some good."

Langley said she began by slipping off her black leather belt, sliding it along her body and dangling it in front of Barry as she told him: "Your friends tell me you're into leather" -- a line she uses in all her performances. She then wrapped the belt around the mayor's neck and placed her hat on his head.

When it was over, she said, an anxious police bodyguard ushered her back into the room so she could unlock the mayor's handcuffs.

She said that Barry then raised his hands over his head and roared: "Free at last!"