The elevator doors parted and out stepped burglar Billy the Kid.

He spotted the television camera immediately and paused a moment, lingering like Cinderella at the top of the ballroom stairs. Two beefy officers at his sides, a police public relations man behind him, Billy raised his manacled hands and poked a fat cigar into his mouth.

"Mind if I smoke?" asked Billy, the man who hours before had been sentenced to 20 years in jail. "I brought a cigar along for the occasion."

His name is William Lee Kidd, alias William Lee Offutt, and he has been labled Arlington's self-styled master thief, a man detectives said had burglarized 3,000 homes and offices around Washington in the last three years.

So last Tuesday, police arranged a press conference to boast of their catch.

The next day, with the memories of news spots on local radio and television still fresh and the rumpled copies of newspaper articles scattered on desks in the squad room, Arlington police began qualifying the information they had released about Kidd, facts taken unskeptically by the press and used to spin a romantic tale of a thief's thief:

At first, police said Kidd committed 3,000 burglaries. Wednesday, though, they were backing off. Said detective Frank Rich: "I hope we didn't lead any members of the media to believe that . . . we've confirmed [his claims]. Some of what he says has been corroborated, but we haven't confirmed that many.

"Let's say he did a total of 300 over a 3-year period. That is a lot for any burglar to get away with," Rich said.

"Our problem," Rich said, "has been trying to distill what is true from what he provides. There is a kernel of truth in everything he told us but it's all in some degree embellished. He really gets off on romanticizing the facts."

Police also said Kidd was a marine in Vietnam, that he served in the Marines as a paratrooper and a medic from 1974 to 1978, spending 1975 to 1976 in Da Nang with the 6th Marine Airwing Division.

But Marine authorities have no record of Kidd. The Marines have no medics, because Navy hospital corpsmen serve the Marines in that capacity. And paratroopers are Army soldiers, though Marine reconnaissance units are trained as parachutists, said a Marine spokesman.

There is no such thing as the 6th Marine Airwing Division either and the 6th Marine Aircraft Wing was deactivated in 1945, said Marine public affairs officer Maj. Fred Peck. And if Kidd was in Da Nang in 1976, he said, "He must have been fighting for the North Vietnamese." Peck said Da Nang was taken by the North Vietnamese in April 1975. The last Marine ground combat units were pulled out of Vietnam in June of 1971, Peck said.

Kidd also asserted that he had "penetrated" both FBI and CIA headquarters on a dare. Spokesmen at both agencies said that is unlikely.

Kidd also told police he had a $1,500-a-week addiction to heroin, cocaine and amphetamines. But Arlington police acknowledged yesterday that in jail Kidd had exhibited none of the violent withdrawal symptoms that heroin addicts usually suffer when denied their drug.

When Kidd was captured on May 13, at a $34.88-a-night hotel on Wilson Boulevard, police found $200 in travelers checks and 800 Susan B. Anthony dollars, alleged booty from an insurance company that had been robbed earlier that evening.

At first, detectives thought they had just an ordinary criminal. But when they got him in for questioning, the 5-foot-3-inch suspect proved "amazing," Rich said.

He talked and talked and talked some more. He gave dates and locations and points of entry. Arlington police were satisfied enough with his testimony to close the books on about 225 burglary cases. D.C. police closed 47, Falls Church 120, Alexandria another 20. Prince George's, Montgomery and Fairfax are still investigating.

Kidd got 40 years, 20 suspended on a guilty plea involving six cases. The Arlington police got a burglar whose notoriety could bring them the kind of publicity that D.C. and Fairfax police received when they apprehended Bernard Welch.

"A lot of these other jurisdictions are somewhat envious of us that we were able to catch him," Rich said. "In order for them to conduct their own investigations they have to come to us now."

"I guess that they probably don't get someone that they can clear as many cases with that often," said a police official from another suburban jurisdiction. "Maybe he's their answer to Bernard Welch. I guess they recognize that it is an attention-getting yarn."

Asked at the press conference who his heroes are, Kidd puffed awhile on his cigar, then said:

"Clint Eastwood, he's bad. Bronson, maybe. And me -- I'm my own hero."