An early morning fire gutted the fashionable 18-room condominium apartment of former Sen. George McGovern in Northwest Washington yesterday. The former presidential candidate's 30-year-old son slightly burned his feet trying to put out the fire, D.C. fire officials said.

The fire, which broke out at 3:10 a.m. yesterday at McGovern's seventh-floor apartment at 2029 Connecticut Ave. NW, caused about $250,000 in damage to the apartment and its contents, according to Battalion Chief Michael Tippett.

McGovern was in Dublin teaching an American history course, according to McGovern's assistant, Ruth Claveloux. McGovern, who arrived in Ireland a week ago with his wife, Eleanor, has not decided whether to return because of the fire, she said.

The fire was caused by a smoldering cigarette left in an upholstered chair, Tippett said. Steve McGovern, who was home alone, was only slightly burned and was not hospitalized, officials said.

There were no serious injuries, but firefighters evacuated the 26-unit building, Tippett said.

The foyer, dining room, living room and main hallway of McGovern's apartment were destroyed by the fire, Tippett said, and other rooms in the apartment were damaged by smoke and water. The other two apartments on the seventh floor, including one owned by Rep. Lindy Boggs (D-La.), were damaged by smoke, and the apartment beneath McGovern's was damaged by dripping water.

McGovern's son, who was house-sitting for his parents, went to bed yesterday morning without knowing the cigarette was smoldering, and was awakened by a smoke alarm in the apartment, fire officials said.

"For awhile, I was trying to put it out myself by throwing water on it, but it was pretty useless," McGovern said yesterday. "It was so hot already."

McGovern telephoned for the fire department, but Secret Service officer Fred Appleton, stationed nearby at the Soviet Consulate, had already notified fire officials.

"When I heard the smoke detector, I woke up my wife and daughter and opened up the door to the hallway, but there was already so much thick black smoke I thought it would be safer to stay in the apartment," said Ronald Linton, who lives on the building's seventh floor. "I had my wife and daughter put their heads out the windows for air."

Firefighters led Boggs and other residents down the building's stairway with gas masks, Tippett said.

Among the residents of the stately building are former Sen. James Abourezk (D-S.D.), D.C. Court of Appeals Judge Catherine B. Kelly; Kennedy Center artistic director Marta Istomin and her pianist husband, Eugene; and Virginia Knauer, special assistant to the president for consumer affairs.

Friends of McGovern described the apartment as well-appointed, with Corinthian columns in a gallery room, a grand piano in the foyer and design elements in velvet and damask. McGovern bought the apartment for $250,000 in February 1980. CAPTION: Picture, Fire that swept former Sen. George McGovern's condominium on Connecticut Avenue NW caused an estimated $250,000 damage. By Larry Morris -- The Washington Post