Twelve persons were injured, two of them seriously, early this morning in a fire that began in an elevator shaft and swept through several upper floors of a 17-story subsidized apartment building in Wheaton.

More than 100 firefighters and dozens of fire trucks rushed to the two-alarm blaze, which broke out just after midnight in a service elevator shaft on the 12th floor of the Rock Creek Terrace Apartments at 12630 Viers Mill Rd. The blaze spread quickly up the shaft and into adjoining apartments on the 12th through 14th floors as heavy smoke billowed throughout all of the upper stories.

One of the seriously injured was a Kensington volunteer fireman who, groping down a smoky hallway, fell four stories down an open elevator shaft. He was in critical condition early today in the shock trauma unit of University Hospital in Baltimore.

The other seriously injured person was identified as a 23-year-old woman resident who suffered face and arm burns. She was listed in fair condition at The Washington Hospital Center.

Several hundred sleepy residents were evacuated from the upper seven floors to the parking lot outside the building, as two police helicopters landed at a nearby church and a shopping center to assist in transporting the victims. The other injured, one an unidentified infant, were said to have suffered mostly minor burns and smoke inhalation and were being treated at several area hospitals this morning.

Bruce Dillon, 21, who lives on the 14th floor, said he was awakened shortly after midnight by a clanging fire alarm. "There were flames and smoke coming through the spaces around the elevator door," said Dillon, who raced back into his apartment to gather some belongings and then made his way with other residents down a stairway to safety.

Another 14th floor resident, Kim Hobson, said "there was smoke all over the hallway. People were streaming down the stairs to get out, yelling and pushing."

Cause of the fire and extent of damage had not been determined early today. Fire officials said the blaze was out in about an hour, and residents of most floors began returning to their apartments at about 1:30 a.m.