Children playing in a laundry room at a Fairfax County apartment complex broke a natural gas pipe there, leading to the explosion and fire that destroyed five units and did about $650,000 in damage, county fire officials said yesterday.

Investigators interviewed children who were playing "on or around" gas pipes in the basement laundry room and broke a pipe, fire department spokeswoman Pam Weiger said. She said that when they tried to repair the damaged line, a second break occurred and the children ran upstairs to notify adults just before the explosion at 7 p.m. Saturday.

Paul Young, a spokesman for Washington Gas Light Co., said the two breaks were in a three-quarter-inch pipe leading from a gas meter to a gas dryer in the basement of the Southern Manor Apartments.

Young said the broken pipe is the responsibility of the apartment management, not the gas company, which owns the pipes leading to the meters inside the buildings.

Gas from the broken pipe apparently leaked into the laundry room, was ignited by an unknown source, and exploded, investigators said. Before it did, Weiger said, several adults alerted by the children started warning their neighbors of the leak, an action, she said, that "certainly saved some lives."

Another adult, James Mills, 27, of Woodbridge, who was visiting the Several adults alerted by the children started warning their neighbors. complex, went in to the laundry room, discovered the broken pipe, heard "a sizzling noise," and was racing up the stairs to call the fire department when the gas exploded, blowing him against the stairwell and shattering the three-story apartment building.

The explosion and fire seriously damaged only one, 30-unit building in the 700-unit complex, but four additional buildings were closed Saturday night, temporarily displacing the occupants of 107 apartments.

Residents were permitted to return to those four buildings Sunday night. Officials condemned the one in which the fire took place, at 7250-54 Fairchild Dr., until its soundness could be determined.

Four people were slightly injured in the explosion and fire, and one firefighter was slightly burned. Fire officials said it was nearly miraculous that no one was seriously hurt.