The minister who conducted Billy Viscidi's funeral yesterday said Mrs. Viscidi told him she believes that her son's death was "probably an accident."

The Rev. Frank Roberston's comments came in an interview after a brief and starkly simple funeral service for the 12-year-old Vienna boy whose body was discovered a week ago in a yellow plastic bag buried in a shallow grave in the family garden.

Earlier in a small softly lit funeral chapel, the minister described Billy as "a sensitive and excepticnally bright young man" whose death was "awful and painful." The ashen-faced Viscidis sat in the front row of the chapel about 12 feet from Billy's coffin which was covered by a spray of white carnations as Robertson delivered a 20-minute eulogy.

Private investigators, who shielded the Viscidis from reporters at the funeral, disclosed in an interview that some of the items found inside the plastic bag with Billy's body were clothes "that didn't fit Billy."

Their statement and the limited amount of information that Fairfax County prosecutor Robert F. Horan Jr. has been willing to disclose have done little to dispel the mystery about how Billy died. Yesterday, citing the funeral and the family's mourning, Horan said he had "absolutely nothing to say" about the case which he has described as "very bizarre."

Robertson, 41, a pastor at All Souls Unitarian Church in Washington, said he learned Mrs. Viscidi's view of her son's death during a two-hour conservation with her and Billy's three brothers, Steve, 16, Larry, 14, and Kenny, 10.

Until then Robertson said, he had never met the family. He said they asked him to conduct the funeral because, as a Unitarian, the family believed he "would respect their Jewish and Christian backgrounds."

Burton Viscidi, a broadcast technican at the Voice of America, is a Roman Catholic, and his wife.I Grace, a computer specialist at the Central Intelligence Agency, is Jewish, the minister said.

Yesterday, Burton Viscidi, looking drawn and pale, left Georgetown University Hospital where he is being treated for a kidney aliment to attend the services. He held his wife's hands during the funeral service and sat with his three sons as Robertson said Billy was a boy "who wished he could have been larger," but who made up for his small stature in "intelligence an patience."

About 60 people attended the funeral at a Vienna funeral home and a smaller number gathered later at Fairfax Memorial Park on the edge of Fairfax City as Billy was buried at the crest of a tree-shaded knoll under a hot, hazy blue sky. Billy's brothers, dressed in subdued casual clothing has somber faces and watery eyes at the graveside service. Larry was crying when the family entered the funeral chapel.

In his eulogy, Robertson said that Billy's family told him the boy once won first prize in a judo contest and he maintained a chart on major league baseball players and their bating averages. The minister mentioned a letter from Billy's fifth grade teacher at Marshall Road Elementary School that described the boy as one who "endeared himself to teachers because of his cooperation."

Billy, after a bicycle accident on May 21, sent a letter to thank a man who held his hand in an ambulance on the way to the hospital, Robertson said.

The Viscidi family has gone through a "tough time," said Robertson, but he said he was "amazed" at Mrs. Viscidi's "inner strength" and at the closeness of the family.

Billy disappeared on July 25 and was thought to be a runaway or kidnap victim until his body was discovered last Saturday afternoon in the family's back yard.

Police said on Monday in a search warrant affidavit they believe Billy died after being assaulted in the living room of his house. An autopsy showed the boy died of a skull fracture caused by a blow to the back of the head.

Attending yesterday's funeral were mourners who have got caught up in the search for Billy and the investigation of his death.

Sgt. Joe Tavares, a 16-year-veteran of the Vienna police force, talked sadly before the funeral about his department's investigation of the case and critics who have labeled the Vienna police work "sloppy."

"It's all over as far as I'm concerned," Tavares said. The detective, who still speaks of the discovery of Billy's body in hushed tones, is no longer working on the Viscidi case. Fairfax County police are now conducting the investigation into Billy's death, which has yet to be classified either accidental or murder.

Tavares said that he and his department did their best in looking for Billy, but said he had often walked past the back yard grave during the 18 days when Billy was believed missing. "You just couldn't see it," Tavares said.

Robert Burgener, who lost his job as a weekend administrator at Georgetown University Hospital due to the Viscidi case, also was at the funeral. "I am here to show that I am still close to the family," Burgener said.

Burgener said he was fired because he allowed a television reporter access to the family and because he told a newspaper, "Mr. and Mrs. Viscidi are resting quietly."