Four persons were burned, two of them seriously, when a cooking stove exploded inside a shed behind a vacant house in Falls Church, fire officials reported.

Officials were investigating the possibility that the four -- none of whom was immediately identified -- were transients who were staying in the shed. Neighbors said that the home at 2805 Liberty Ave. has been unoccupied for the past year and that there have been problems with transients living in the shed.

The explosion of the butane- fueled cooking stove occurred around 8:15 p.m., and the resulting fire was brought under control in less than five minutes after firefighters arrived, a Fairfax County fire official said.

"It was more a medical problem than a {fire} containment problem," the spokesman said. The cause of the explosion was not immediately known.

Three of the injured were flown by helicopter to the Washington Hospital Center and the fourth person was taken by ambulance to Arlington Hospital, the spokesman said.

A nursing supervisor at the hospital center said a man and a woman were in critical condition with burns on their faces and chests and smoke inhalation. A second man was admitted in fair condition with minor burns to his arms and legs.

The man taken to Arlington Hospital was reported in fair condition with superficial burns.