An elderly woman testified today that she saw 20-year-old Larry Rogers "slumped over" in the front seat of a green station wagon driven by murder suspect Wayne B. Williams on the last day Rogers was seen alive.

Nellie Trammell, who said she had seen Williams several times before that day but did not know his name, testified that Williams cut in front of her while she was trying to make a right turn near Rogers' house on March 30, 1981.

Trammell said Williams' station wagon slowed as it passed her car. "I looked at this man's face and Larry Rogers was in the seat and he was like this," she said, leaning against the side of the witness stand and crossing her wrists at her waist.

Rogers' decomposed body, clad in blue gym shorts with an undershirt stuffed in the waistband, was found April 9, 1981, in an abandoned northwest Atlanta apartment. He had been strangled.

The Rogers' case is among nine deaths that prosecutors have introduced into Williams' trial on two other murder charges, as evidence of an alleged pattern of slayings. Judge Clarence Cooper has agreed to let the prosecution introduce evidence on 10 slayings, in addition to the murders of Nathaniel Cater, 27, and Jimmy Ray Payne, 21, to show a "pattern" in the crimes.

Williams has denied knowing any of the 28 young Atlanta blacks whose deaths are being investigated by a special police task force and the FBI. Trammell said she recognized Williams as a man she saw with cameras and a camera bag at the Techwood Homes housing project earlier that spring.

At the housing project, Trammell said she saw Williams by a white station wagon and thought he was "a newsman." Another witness has testified that Williams drove blue, green and white station wagons.

Trammell said she had picked out Williams' picture from a police photo lineup, apparently after Williams became a suspect in late May, 1981, but before his picture was shown on television. "I didn't know who that was until they put his picture on the news," she said.

She also said she saw Williams at Rogers' funeral and the funeral of Eddie (Bubba) Duncan, a 21-year-old Techwood resident whose body was found in the Chattahoochee River March 31, 1981. Judge Cooper, however, instructed the jurors to disregard the reference to Duncan. His case has not been introduced into Williams' trial.

Trammell tended to confirm testimony earlier today by a 35-year-old former heroin addict who admitted that he had smoked marijuana with his morning coffee before going to the courthouse.

Tilbert Bayhnam, who told defense attorney Alvin Binder he had smoked "herb" (marijuana) for 23 of his 35 years, said Rogers bought a marijuana cigarette from him and then got into a car with Williams one day last spring.

Bayhnam, who said his nickname is "Cool Breeze," testified that Rogers said he wanted the marijuana because "me and my friend in the car want to get high."

Bayhnam said he asked Rogers whether he was being set up for a drug arrest and Rogers replied, "No, he's my friend, he's my buddy."

Another witness, Charmine Kendrick, said she saw Williams with 15-year-old Terry Pue about a week before Pue's body was found last January.

Under cross-examination, however, she said she saw Pue in April.