A badly decomposed body, believed to be that of missing 12-year-old Billy Viscidi of Vienna, was discovered yesterday afternoon stuffed in a plastic bag and buried in a shallow grave at the edge of the Viscidi backyard.

Although positive identification of the young male body had not been made last night, both Vienna town and Fairfax County police said they assumed it was Viscidi, missing for the past 19 days.

The body was uncovered after friends of the boy's mother spotted what neighbors said was "some earth that didn't look right" behind a row of corn in a small garden on the Viscidi property. The grave, three feet deep, was about 46 yards from the family home.

A friend stuck a shovel into the earth, it hit something hard and the blade broke, neighbors said. Police were then called to the home and uncovered the body.

Fairfax Commonwealth's Attorney Robert F. Horan said last night that he had been contacted by police after the body had been found. "What we have right now is very sketchy." he said.

"It's too early to talk about suspects at this point, but it's fair to say that what happened today certainly isn't a normal situation," Horan said. "But to say anything beyond that at this point would be purely speculative."

Viscidi has been the subject of a massive police search in Northern Virginia since disappearing the morning of July 25. Last week his mother, I. Grave Viscidi, went on television and made an emotional appeal for help in locating her son, one of four brothers.

"I want my boy. If Billy is able to come home, we want him home." she told reporters. "Billy, I'd like you to come home if you can. We love you and this is your home. We want you back."

Posters for the missing boy have been placed by police throughout the Virginia suburbs. Mrs. Viscidi, a computer programmer at the Central Intelligence Agency, asked some co-workers to come to the home to help continue the search yesterday.

They searched the backyard again, although numerous backyard searches previously had turned up nothing suspicious.

According to Fairfax Police Lt. Jackie Watts, the coworkers looked several place, including a crawl space under a two-year-old addition to the Viscidi house.

After the grave was discovered police found the body, which Watts said "had been decomposing for at least several days," in the shallow grave.

The grave had been dug almost at the corner of the Viscidi property line, between cornstalks and a row of thick hedges.

Police said the body was so badly decomposed that the only way they would be able to make a positive identification would be to have the family dentist examine the boy's teeth.

Heavy rains of Friday night and recent days made it impossible to pinpoint the time the grave had been dug, police said.

"It's very hard for us to know much of anything at this point," Watts said. "The way the grave was situated in the garden it's possible that searchers could have been walking right past it. There've been so many searches in the past few days it's hard to tell if the body had been there before or not."

Neighbors said that police had searched the yard on Friday. Watts said he knew the yard had been searched then but did not know who conducted the search.

He said there are no suspects in the case at the moment. "We'll talk with the entire family and anyone who knew the boy," he said. Burton Viscidi, the boy's father, a broadcast technician for Voice of America, re-entered a hospital on Thursday for minor surgery.

He was in the hospital, having just had a kidney stone removed, when Billy disappeared. The elder Viscidi left the hospital at that point to help in the search and, according to his wife, "the whole operation will have to be redone," because of the physical stress and mental strain he had been under.

Police would not comment last night on whether the body was clothed or if it had any marks on it, but did say there were investigating the death as "suspicious." Homicide detectives were assigned to the case.

Billy Viscidi, 4 feet 6 inches tall weighing 72 pounds, was to enter the eighth grade at Luther Jackson Intermediate School this fall.

His father has said he was "very close," to brothers Steve, 16, Larry, 14, and Kenney, 10. Larry told police Billy ate breakfast on the 25th, then "just walked down the driveway, took a left and headed toward Nutley," wearing a red tank top and cutoff blue jeans.

The body was removed from the scene after preliminary examination by medical examiner Dr. Claude Cooper. An autopsy is expected today.

Mrs. Viscidi left the house about 6 p.m. with friends. Later she was taken to Georgetown University Hospital where she was admitted to spend the night with her husband.

Discovery of the body left people in the neighborhood of handsome homes much like the Viscidis' one-story brick rambler in shock.

"I guess we all thought something like this might have happened," one neighbor said. "But the reality of it didn't hit until today."

A boy fitting Viscidi's description, accompanied by a muscular young man, was seen in a McDonald's Restaurant at Fairfax Circle in Fairfax City that afternoon by a woman. From her description police made up composite drawings that were used on posters distributed all over the northern part of the state.

Last week, Vienna Police Sgt. Joseph Tavares said Vienna police suspected a man arrested in Arlington on a sodomy charge and had questioned him in the Viscidi case. Arlington police said last night, however, that they had not been contacted by Vienna police all day.

None of the family members could be reached yesterday for comment. The brothers were reported visiting in New York state.