Harry James Bennett, looking drawn and pained during three hours of testimony at the murder trial of 10 young people, described in detail yesterday how he and about a dozen others repeatedly punched and kicked Catherine L. Fuller as she was pushed along a Northeast alley and then dragged into an abandoned garage.

The packed courtroom in D.C. Superior Court hushed when Assistant U.S. Attorney Jerry S. Goren asked Bennett, who has pleaded guilty to killing Fuller, what happened next in the garage where Fuller's body was found later that evening, Oct. 1, 1984.

"We were all standing around and that's when Levy [Rouse] went and got a pole . . . ," said Bennett, 19, as he held two fingers in an inch-wide circle to demonstrate the width of the pole. "The lady was lying down on her back . . . and Steve [Webb] and Calvin Alston had her legs . . . . That was when he [Rouse] was beginning to stick the pole up the lady . . . "

Did you hear anyone saying anything? asked Goren. "Yeah . . . Snot Rag [Timothy Catlett] said stop . . . and I heard Calvin [Alston] and Steve [Webb] say, 'Push it farther up.' "

"Did Mrs. Fuller say anything . . . ? " Goren asked.

" 'Stop,' " Bennett replied in a whisper, breaking into tears as a moan erupted in the courtroom.

The testimony of Bennett, who has pleaded guilty to manslaughter and robbery, was the most damaging yet in four days of prosecution testimony in the tense and emotional trial of nine young men and one young woman who have been charged with first-degree murder, armed robbery and kidnaping in the death of the 48-year-old mother of six.

Bennett, who was living only a few blocks from the alley in the 800 block of Ninth Street NE at the time of the slaying and who said he knew most of the defendants, repeatedly went down the two rows of defendants yesterday reciting in clear detail each one's participation in the beating or robbery.

Bennett said only one of the defendants, Clifton E. Yarborough, 17, was not present in the alley or in the garage during the beating, or at the Eighth and H street park, where Bennett said most of the defendants were gathered when they left to follow Fuller.

Bennett also said that one of the nine defendants, Felicia Ruffin, 17, did not beat Fuller but that Ruffin was standing in the garage and accepted a ring taken from Fuller.

During a break in Bennett's testimony, Ray Yarborough, whose brother Clifton is on trial, said he had sighed a "whole lot" when Bennett said Clifton Yarborough had not taken part in Fuller's death.

Bennett said he was sitting in the park on Oct. 1, 1984, when he saw Calvin L. Alston, 20, Levy Rouse, 20, Russell L. (Bobo) Overton, 26, and Steven L. Webb, 20, cross H Street and follow a "lady" around the corner of Eighth Street, moments after Alston had said "let's go get that lady." Others, he said, followed, including: Catlett, Alphonso L. (Monk) Harris, 23, Kelvin D. (Hollywood) Smith, 20, Charles (Fella) Turner, 21, and his brother, Christopher D. (Chrissie) Turner, 19.

Alston pleaded guilty two weeks ago to second-degree murder. The other eight, plus Yarborough and Ruffin, are on trial this week. Testimony by Alston and Bennett, who agreed to testify for the government as part of their plea bargain, is the core of the prosecution's case.

After the group crossed the street, Bennett said, he went to the corner "to see if the police were coming" and he, too, walked to the alley. When he arrived, he said three of the young men already were "beating the lady" and he joined in.

"I beat and kicked and hit the lady," Bennett said. "Did she say anything?" Goren asked. "She was hollering for help," Bennett replied. He said Fuller was then pushed down in front of the garage where the beating continued. "At that point in the alley mostly everyone was hitting and kicking her," he said.

"Snot Rag?" asked Goren, going down the list. "Yes, sir." "Monk?" "Yes, sir." "Bobo?" "No, sir, he didn't hit or kick the lady at that point." "Levy?" "He hit and kicked the lady . . . . "

Bennett said Overton then dragged Fuller into the garage where the beating stopped and Rouse picked up the pole.

"At that point, that's when I left," Bennett said. A medical examiner has said a pole was thrust so deeply into Fuller's rectum that her colon was pierced.

Defense lawyers seemed unnerved by Bennett's testimony and his ability to withstand cross-examination that included repeated questions about when Bennett "murdered that woman."

Bennett denied he had agreed to cooperate with police to stay out of jail after being arrested in April on a cocaine charge. Bennett was released from jail after his February arrest. He said he expected to receive a prison term of 31 years when he is sentenced in December.

"I wanted to tell the truth because I knew I was guilty," he said. "I knew if I was sitting over there like they're sitting over there I'd get 20 to life," the mandatory prison term for first-degree murder before becoming eligible for parole.

Bennett's testimony left unanswered the question of why a group of young people would commit a crime that has been called one of the most brutal in the city's history.

"She was just a little lady and she was hollering for help and you just punched and punched," asked lawyer Frederick Sullivan. "Yes, sir," replied Bennett. "What was your object? What did you hope to accomplish?" Sullivan asked moments later. "I don't know," Bennett answered.