A maid sweeping a front walk last Dec. 5 near the Northwest Washington home of cardiologist Michael Halberstam testified yesterday that she watched a man with a mustache drive by Halberstam's house in a silver Mercedes-Benz hours before the physician was fatally shot when he returned home and surprised a burglar.

"I saw the silver Mercedes-Benz drifting slowly down the intersection where I work," Mamie Stallworth nervously told a D.C. Superior Court jury. "He made a brief stop at 2806 [Battery Pl. NW] -- the Halberstams.'"

Stallworth, who works for one of the late Halberstam's neighbors, said she later shouted at the man, whom she subsequently picked out of a police lineup. The man she selected was Bernard C. Welch, who is accused of murdering Halberstam.

Stallworth's key testimony came on the third day of Welch's murder trial, which at one point yesterday took on the appearance of a jewelry auction, with a string of Northwest Washington residents identifying scores of gold and silver jewelry items that Welch allegedly stole during burglaries of their homes on Dec. 5, and a D.C. auctioneer appraising the value of the items at several thousand dollars.

FBI agent Philip Chaney also testified that his .38-caliber revolver was stolen from his home last Nov. 10. A government ballistics expert is expected to testify today that the gun was used to shoot Halberstam. The prosecutors then are expected to rest their case against Welch, who faces murder, burglary and gun charges.

However, it was Stallworth's testimony, which Welch's attorney claimed he will discredit today, that directly places Welch at the scene of the Halberstam killing.

Stallworth said that, at 1:40 p.m. on Dec. 5, she saw Welch park outside Halberstam's home, look at the house and drive away. The government contends that Welch was casing the house for a later burglary attempt.

Four hours later, Stallworth said, the silver Mercedes appeared again, blocking Stallworth's exit from the tiny cul-de-sac where Halberstam's house was located and from where she was heading home.

"[The car] was . . . too close, so I wouldn't be able to reach the intersection to go out," Stallworth said. "I eased up, honking my horn. He didn't respond, so I honked my horn again."

Finally, Stallworth said, she rolled down her car window and yelled: "You stupid dummy, can't you move your car so I can come out?"

At a police lineup about a week later, the videotape of which was shown in the courtroom, Stallworth instantly picked out Welch. "That was the same man," Stallworth testified in response to queries by Welch's attorney, Sol Z. Rosen. "I'm very positive it was."

"We got a lot of stuff that will knock her [testimony] out," Rosen later told reporters. "We will prove [Welch] was in Virginia till about 5 p.m., then downtown."

Welch sat impassively as he watched prosecutors play a videotape of Elliott Jones, Halberstam's widow, listening to Welch and 11 other men at a police lineup repeat a threat she heard the night Halberstam was killed: "Lie down, or I'll blow your f----- head off." Jones selected three of the voices, one of which was Welch's.

Welch's alleged burglary victims identified more than 175 items that were found in Welch's Mercedes. Included were gold and silver jewelry, as well as a dentist's denture mold with gold caps and a copy of Money magazine.

Some of the witnesses seemed embarrassed at the extraordinary array of items spread before them. The daughter of one burglary victim, who said she returned home to find her house ransacked, blushed as she identified a pin that was a gift from a boyfriend.

Another burglary victim smiled sheepishly as she explained that a silver hog allegedly taken by Welch from her collection of more than 30 pigs was an anniversary gift from her husband. "I wasn't too flattered when I got it," she admitted.

"Is there some reason you have 30?" Rosen quipped, drawing laughter from the more than 100 spectators.