Prince Willian County police are investigating the possibility that five powerful blasts that have rocked the woods near Dale City in the last two weeks are the work of a gang of neighborhood youths.

Investigators initially assumed that the bombings were the work of an emotionally disturbed Vietnam-era serviceman who had built military-style bunkers in the woods and set off blasts that created brilliant orange fireballs. Police still consider that a possibility.

But regardless of who is to blame, the residents of Dale City, 30 miles south of Washington, say the bombings have brought fear and uncertainty to the area. "Our peaceful little neighborhood just went caflooie," as resident Barbara Stuck put it.

The first indication of possible gang involvement came May 19, three days after the first explosion. Police officer Greg Garret, who works out of Gar Field High School, found in his school mailbox a semiliterate and badly typed note listing ingredients for an explosive.

The note concluded: "Put across small well used path for person to trip, this should throw out the shrapnal [sic] at chest level."

That same day, Jan Miller, coach of a girls' softball team that plays in a park next to the woods not far from where the explosions occurred, told a local newspaper she came across two youths who told her they were playing with gunpowder, a possible ingredient of the pipe bombs that exploded. On another occasion, the same youths had fishing line and clothespins, parts that make up the triggering mechanisms of pipebombs, she said.

When she asked them what they were doing, Miller told reporters, one boy answered, "What do you think we're doing, lady? We're making bombs."

Police have declined to comment on Miller's story.

Police documents say that the explosive devices that left six-inch holes in the forest floor could have been concocted by following directions in publications of "subversive groups" that "graphically detail the manufacture of . . . booby trap devices." The documents say they were constructed of "accessible accessories that are common in all hardware stores and/or hobby stores."

Some sources close to the investigation say that three Vietnam-style bunkers discovered by police last Sunday look highly professional, possibly the work of a Vietnam veteran. The central bunker, the sources said, is topped with heavy logs packed with dirt. Hidden with leaves in a deep thicket, the central bunker covers the avenues of approach at the junction of three paths that lead to a hill. Trail markers of vines and sticks stripped of bark were placed to mark booby traps, a technique that was used in Vietnam.

And a 40mm "blooper" granade, designed to send shrapnel whizzing into enemy troops at 20,000 feet per second over a 100-foot radius, was discovered Monday beside a road three-quarters of a mile from the bunkers.

"Whoever it is, he certainly doesn't work like a kid," says County bomb expert Michael Null, a 10-year Marine Corps veteran who served two tours in Vietnam.

But Anna Sapp, who leads the Prince William Volunteer Junior Corps -- a hiking and ecology group with about 20 teen-age members that recently renamed itself the Dale City Hikers With No Place to Hike after police closed the woods -- say she believes that youths were involved, members of a tough-talking gang of street-wise hoods who meet in the woods.

County police juvenile investigator Gene Barnhart said he's been talking to Sapp and that "she has said some things that came out to be truth . . . given us information that has checked out at this point.

"Anywhere you go you have gangs," Barnhart says. "You have a group of kids here getting together . . . most of the things they do are not right by law." Barnhart refuses, however, to comment further, fearing "it might hurt our case."

Residents say it is possible that police could view the gang's work as professional because they have access to military handbooks and material supplied by several relatives recently discharged from the service. Police division commander Capt. J. A. Sindlinger agrees. "I think [the bunkers] were built by kids," he says.

Sapp said she wonders, too, why a commando would take time to destroy a fort her own group recently built. It was wrecked, she said, sometime after a blast was reported on Sunday.

For now there are no answers. Police continue to investigate. And in the neighborhood, there is talk of confrontation. "If one kid comes out with powder burns again," said Sapp, "there's going to be a war . . . "I'm not going to stay locked out of the woods forever," she said.