A stubborn fire on the top floor of a condominium apartment building in Adams-Morgan raged for almost three hours yesterday afternoon, at times covering blocks of Northwest Washington with thick, black smoke.

The blaze, described as one of the most challenging for the fire department in recent times, was limited to the top floor of the building at 1801 Calvert St. NW, which was renovated about three years ago and converted to condominiums.

The few owners and tenants in the building escaped unharmed, and fire officials said no one was injured. But as word of the fire spread, primarily through telephone calls from the management company, those who live in the six-story building arrived and watched in disbelief as flames shot from the roof.

A woman stood on the corner and sobbed. Others embraced, and still others speculated about the damage to apartments on the lower floors. Some approached firefighters and quietly asked when, or if, they would be allowed back in the building.

But by 4 p.m., after six water cannons had poured millions of gallons into the building, it was clear that the damage would be extensive and the building uninhabitable. Many were worried about pets.

"My cats are up there," said Marlene Desmond, whose apartment is on the fifth floor. "I don't care about my possessions. I just care about my cats."

The three-alarm fire was reported at 1:29 p.m. and drew more than 150 firefighters from eight of the District's 15 fire companies. Several blocks were closed to traffic, and the spectacle drew several hundred people.

The building, an elegant, triangular structure at the intersection of Calvert Street, Lanier Place and Adams Mill Road, at times was wrapped in dense smoke.

Fire officials at the scene said it would take some time before a cause is found. Early speculation was that a small fire in a duct leading from a dryer on a lower floor had spread to the roof.

At 2:05 p.m., 35 minutes after the fire started, an order for firefighters to abandon the building was given and then suspended. At 2:25 p.m. all firefighters were evacuated and water cannons, mounted on six ladders, began working. The fire nevertheless spread to the rear of the top floor, and several firefighters expressed frustration, saying they would have extinguished the blaze if allowed to remain.

But Fire Chief Ray Alfred said concern that the roof might collapse played a role in the decision to evacuate the firefighters. About 30 air-conditioning units were on the roof, contributing to the hazard, he said.

Residents, who were told they would not be allowed back in until at least today, were put up in two area hotels last night by the Red Cross.

But at least some of the residents got a bit of good news. Firefighters, going apartment to apartment last night, reunited 10 cats and one bird with their owners. There were no reports of pets being hurt or killed in the fire. Staff writer Debbi Wilgoren contributed to this report.