The no-name garage on First Street SE was a busy place last year, taking in more than 100 cars. Word was out that the New York owner, Mario, was very willing to buy stolen cars, no questions asked. Mario had cash and he smiled a lot.

Yesterday, D.C. police introduced Mario as Officer Corpus Garcia. He and other members of the Repeat Offenders Project had completed a sting operation that netted 119 stolen cars valued at $1.5 million and led to the indictment of eight adults and eight juveniles. Police said up to 45 arrests are expected in the case.

D.C. Police Chief Maurice T. Turner Jr. hailed Operation Kill Joy as an important part of the city's anticar theft program, which substantially reduced the growth of car thefts in the District last year compared with the three preceding years, when car theft was said to be at epidemic levels. Most of the city's efforts have been directed at reminding people to lock their cars.

"The increasing spiral of stolen cars has been broken," Turner said at a news conference yesterday, noting that last year's increase was only 3 percent as compared with a 22 percent increase in 1986.

The sting operation was financed partly with contributions from several insurance companies, including Continental Insurance, which has financed 13 similar operations in other parts of the country.

The Repeat Offenders Project commander, Inspector Edward J. Spurlock, said the sting was valuable because "we were able to stop 45 people from stealing cars for at least a short time at no cost to the city."

Spurlock said the officers bought the cars, many of which were Trans Ams, Camaros and other sporty cars, from men and teen-agers who came to the one-story garage in an industrial section of Southeast Washington between June and November of last year.

The building at 1307 First St. SE, a former legitimate garage, was renovated to create secure areas for a team of officers to operate video cameras and record every transaction.

Garcia and three other officers presented themselves to the car sellers as New Yorkers who had come to town to buy stolen cars.

Spurlock said the sting officers were well protected at all times by both the officers monitoring the video cameras as well as by a backup squad outside the building.

He said they were concerned someone might try to rob Garcia.

"One man came in with a gun stuck in his waistband but he didn't try to use it," Spurlock said.

The cars brought to Garcia included three Mercedes-Benzes, four BMWs and one Volvo.

They and all the other cars were bought for an average price of $307 each. Garcia, who was a store manger in Puerto Rico before joining the police force three years ago, said he enjoyed bargaining with the alleged car thieves to see how little money they would take.

"One man said he wanted $2,000 for a Mercedes, but I talked him down to $400," said Garcia. "He didn't like it but I told him, 'Take it or leave it.' He took it."

Spurlock said the department was concerned that it might create a market for stolen cars and told officers to refuse to buy any more than three or four cars from any one seller. He said many of the customers were already known to the police as repeat offenders for various crimes.

Garcia said if a customer started showing up too often, he would meet them at the door and say, "I don't want it, I don't need it. Take it away."

Spurlock said about one-third of the 45 persons who sold them cars have been arrested on warrants charging them with interstate transportation of stolen vehicles or trafficking in stolen property. He said custody orders, the equivalent of arrest warrants, have been issued for eight juveniles including two who are 13 years old.

Spurlock said the investigation is continuing and that police expect to eventually arrest all 45 people allegedly involved in selling the cars.