A fire at the city-owned Roosevelt Hotel for Senior Citizens in Northwest Washington last night destroyed a fifth-floor apartment, sent one woman to the hospital for treatment of smoke inhalation and led to the discovery of a dead tenant in an apartment next door, fire officials said.

The body of an elderly man, whose identity was withheld until relatives could be notified, was discovered in a bed in Room 529, next door to the burning apartment, said Capt. Theodore O. Holmes, a D.C. Fire Department spokesman. The cause of the tenant's death was not known, but Howard E. Dixon, assistant chief of fire operations, said the man appeared to have died before the fire started.

A night manager at the hotel, who would not give his full name, said other residents reported seeing and talking to the man earlier in the day. The cause of the fire and the man's death were under investigation.

Firefighters arrived at the eight-story building at 2101 16th St. NW after receiving an alarm at 8:19 p.m., fire officials said. The fire was confined to Room 528, a two-room apartment, but 15 residents were evacuated to the lobby. Fifty firefighters extinguished the blaze in about 20 minutes.

One resident, Elizabeth Cochrane, 72, was taken to Howard University Hospital and treated in the emergency room for smoke inhalation, said Charles Johnson, the hospital's night administrator. Cochrane was listed in stable condition.

None of the other approximately 175 residents in the 388-unit building were injured.

The fire destroyed the apartment of Gene A. Brady, 71, who said he has lived at the hotel since July 1985. Brady, a World War II Marine, said he had spent about an hour in the hotel's first-floor lounge reading about World War I.

"I walked upstairs and opened my door and smoke poured out," he said. "I came down here and reported it to the desk."

Brady and fire officials said they had no idea how the fire started. Brady said he smokes a pipe, cigars and cigarettes, but that he didn't think they were a possible cause of the fire. "I don't think so at all, no. I've always smoked in there."