Fairfax County police have discovered the frozen body of a 19-year-old Reston man covered with snow in his sleeping bag in woods near Lake Anne.

The body of John Shepard, who according to his father had a history of mental illness and was without a steady job or fixed address, was found Saturday morning 200 feet from a medical office building and three blocks from his father's house.

Police, awaiting results of an autopsy performed yesterday, said they suspect no foul play in the death and attributed it tentatively to exposure in Washington's 15-degree winter elements. The body apparently had been there several days.

"We understand he was in a sleeping bag, which [police] said would normally be good protection," said the boy's father, William Shepard, a retired Army lieutenant colonel. "But with the extremely cold weather, it may not have been enough."

John Shepard had spent most of his life moving from one home to the next, his father said. Until a few days before his death, he had been living with friends in Herndon. But because he wasn't included in the rental arrangement, Shepard, who loved to hunt and camp, had to leave.

Why he walked nearly 100 yards into the woods to bed down in bitter cold, however, remains a mystery.

"We really don't know what he was doning," Shepard's father said. "My wife had worried about where he was living and had said that we should go find him and insist he stay with us. But we didn't have any contact with him."

For several years, the father said, Shepard had spent long periods of severe withdrawal. He had been working odd jobs at the time of his death. He was recently discharged honorably from the Army after his record of institutionalization at a private psychiatric facility in Rockville -- where he was an habitual runaway -- prevented his receiving a security clearance.

"He was very proud that he had gotten an honorable discharge," William Shepard said. "He was very independent.

John Shepard grew up "very friendly and happy and gregarious," his father continued. But as he grew older, he became an increasing discipline problem in school who "sort of built a wall around him that grew as time went by."

"I think," said Shepard, "what it might have boiled down to is that I've been married several times and he was disappointed at having several parents and gradually grew not to trust people."

While the family was stationed in Germany, he said, doctors recommended John Shepard be institutionalized. He was sent to Chesnut Lodge in Rockville.

For some time, however, he had dreamed of joining the Army, like his father. "We were looking for something for him to be successful at that he enjoyed doing. He wanted to work with the missiles in Europe," the elder Shepard said.

When he reached 18, Shepard released himself from Chestnut Lodge, his father said, leaving for California for a time to live with his mother before enlisting.

Once in the Army, he was forced to leave after a few months when his psychiatric record was discovered.

Back in Washington, he chose to live with friends rather then with his father, who was about to remarry. When his latest arrangement fell through because of a conflict in his friends' lease, "he came over here several times. We told him he would be welcome here. But he just came by to wash clothes or eat a meal or pick up some mail."

Shortly before his death, family and friends said they had noticed some improvement in John Shepard. "In the last few months," his father said, "people who knew him said they saw a spark of the way he used to be and he was trying to bring it back. But it was six or eight years of habits to overcome."