It has been nearly three weeks since 17-year-old Jeff Filmeck and his brother Jim, 18, vanished on a canoe trip on the Occuquan River along the southern rim of Fairfax County.

Their father says his "guts nearly spilled out" when, in a lonely search of the river later, he found a watersoaked tennis shoe with the laces tied, and Jeff's military field jacket.

John Filmeck, 42, a General Services Administration communications specialist who lives in nearby Woodbridge, has fiercely refused to quit the search for his sons, though he believes they must have drowned. "If I have to bring them home myself, if that's what it takes, that's what we'll do," he says.

But there is an air of mystery to the disappearance. "It's a very, very strange situation," says Haynes Davis, principal of Woodbridge High School, where Jeff was a senior and Jim a 1979 graduate. "There is a lot of speculation as to what might have happened. 1It will be awhile before we know, if we ever know."

Prince William County police, assisting in the search effort, have ruled out foul play, but Filmeck says "anything is possible."

He says his sons left $100 and two paychecks on their bedroom dressers when they departed at 7 o'clock on the clear, sunny morning of March 8, and Prince William police agree there is no reason to believe the teen-agers had run away.

Yet Filmeck is nagged by the fact that their bodies have not appreared, although drowning victims normally surface within seven to 10 days. He is also aware that his sons were well trained to handle themselves on the water.

Jim and Jeff Filmeck were not Sunday boaters but experienced canoeists, he says. They were trained in how to empty the canoe of water if it did overturn, and knew to stay near the boat in the event of an accident. Their canoe, a Grumman, was a stable, white-water craft -- the "Cadillac of canoes," their father says.

Jeff was a certified scuba diver; Jim was described as an excellent swimmer. Both were described by friends as "bona fide water lovers." Both young men were employed by the Woodbridge-based Marine Structural Applications Co., which builds and repairs docks in Virginia and Maryland.

Filmeck's ordeal began innocently when his sons woke him to say good-bye. "My wife and I were still asleep," he says. "They stuck their heads inside the bedroom window and said, 'See you at suppertime.'. . . That was the last time I saw them."

Filmeck says he wasn't worried when sunset approached and his boys had not returned.

By 10:30 that evening, Filmeck was on the telephone to the Prince William County police department. A thick fog rolled in as a U.S. Park Police helicopter battled winds gusting to 35 mph to flash spotlights into the Occoquan's murky brown water until 2:30 a.m.

Rescuers that later included the Prince William County and Fairfax County fire departments, helicopter pilots out of Fort Belvoir, and Virginia Game Commission boaters have found nothing more than the swamped, 17-foot canoe that the brothers had purchased a month before. The craft was found one-quarter mile upriver from the old Ryan's Dam near Fountainhead Park.

At the time of their disappearance, a small army of state, federal and local officials were struggling to contain a kerosene spill that had fouled Bull Run a few miles upriver from Ryan's Dam.

"One of the first things we checked was whether the kerosene recovery people saw their aluminum canoe since they were busy adding flotation collars below Bull Run Marina," said Prince William police Lt. Adrien Lemmers. "They didn't see a thing."

Lemmers speculated that the extremely cold waters of the river may have prevented the youth's bodies from floating to the surface.

"The game wardens were telling us that dead fish from the kerosene hadn't surfaced because the water was as cold as 35 degrees near the bottom," Lemmers said. "If they spent any time in the water they probably died of hypothermia," a condition in which paralysis and death results from prolonged exposure to extreme cold.

The river is as crooked as a snake," Lemmers continued. "And there are so many coves and inlets filled with logs and debris. We don't even know where the canoe capsized."

Lemmers said police dogs traced the route from where the brothers left their pick-up truck on the Prince William side of the river and carried the canoe to the water, but the trail ended there.

Filmeck, who called in 10 relatives to help him search the river and the banks, has been miffed at the extent of the rescue efforts thus far.

When divers from the Prince William and Fairfax County fire departments arrived at the scene recently, they saw the zero visibility of the water, knew about a strong and dangerous current flowing through a hole in Ryan's Dam, and refused to order their people under the water.

"It was too dangerous for them," Filmeck said bitterly. "I've got a close friend from Pensacola, Florida, flying in tonight. He said he was going down. I knew he would."