A powerful explosion yesterday rocked the same wooded area of Dale City where two teen-agers narrowly escaped serious injury May 16 after stumbling across a booby trap wire that detonated a pipe bomb.

The latest explosion and the subsequent discovery of a highly explosive antipersonnel grenade followed by a day the discovery of three military-style bunkers in the same woods.

Police said residents near Garfield Park described the 2 p.m. blast as "one hell of an explosion" that shook windows and was accompanied by a brilliant flash of light and clouds of smoke.

Investigators said they thought TNT or a military C4-type explosive was the source.

At 4 p.m., police said, a resident of Garfield found a 40-mm grenade near Darbydale Road and brought it to police.Such grenades, used in Vietnam and nicknamed the "blooper," according to bomb squad commander Michael Null, throw fragments 100 feet upon explosion.

The bunkers discovered Sunday were said to be about four feet square, four feet deep and lined with logs. "They are reinforced shelters resembling the kind of military bunkers used in Vietnam," said Null, an ex-marine who served in Vietnam for three years.

"Whoever it is that built them has seen a professional handbook on how to build bunkers and foxholes," Null said.

Capt. J.A. Singlinger of the Garfield substation hesitated to agree with Null's characterization of the holes. "They are holes in the ground," Sindlinger said. "Military veterans call them bunkers, kids call them forts . . . We've had kids building forts back there in the woods for years." f

"It wasn't a kid's fort," Null countered.

Sindlinger said "it would be speculation at this point" to assume a connection between the holes, several recent bomb blasts, and reports that residents have seen a man wearing combat fatigues and green face paint emerging from the woods carrying a shovel on several occasions.

Police have advised residents to stay out of the dense woods of Cloverdale Park since May 16, when two boys tripped across a thin wire that detonated a plastic pipe bomb. One boy received minor powder burns on his arm. The other was unhurt.

Residents reported at the time that at least once they had seen a man in military fatigues pointing a rifle or shotgun at children on a baseball lot at the park. Police searches at the time found nothing.

Then, last Saturday night, residents near the park reported seeing a brilliant orange fireball over the area.

After combing the area on foot Saturday night, county law enforcement officers called in a state police helicopter and searched the area again on Sunday, this time finding the three holes.

Police also found honeysuckle vines used as warning marks on several paths that connected the holes, a tactic commonly used in Vietnam "to prepare for an ambush," Null said.