At least five fires believed caused by arson broke out within a few square blocks in Georgetown early yesterday, awakening frightened residents, damaging vehicles and buildings and critically injuring a 36-year-old man who lives above a Wisconsin Avenue store.

The first of the fires was reported in a small truck in the 3100 block of O Street NW at 3:22 a.m., and before firefighters left the scene they were called by citizens to deal with a blaze at a house a few doors down the street.

Minutes later, a two-alarm fire was reported around the corner where flames spread from the rear porches of two adjoining buildings in the 1400 block of Wisconsin Avenue to the buildings themselves, causing substantial damage. Barry Alpert, who lives in an apartment above a store in one of the buildings was burned severely over much of his body. He was reported in critical condition last night at the Washington Hospital Center.

At 5:23 a.m., about 90 minutes after the Wisconsin Avenue blaze, firefighters were called to the 1300 block of 29th Street NW, three blocks away, where two parked cars were ablaze.

"It's obvious" that the fires were deliberately set, said Lt. Calvin J. Wilson of the 2nd Police District. "I can't see how it could be anything else" when so many fires break out in so small an area in a two-hour period.

"You feel vulnerable," said Rebecca Hardy, 21, who lives at 3146 1/2 O St. NW, the site of one of the fires. "All these fires," she said, "it doesn't look like an accident."

She said the fire at her building apparently began on a sofa outside the back of a basement apartment. The couch and a fire escape were damaged.

Smoke damage to the building itself, residents said, was limited by the quick response of firefighters originally summoned to deal with the blaze in the truck parked nearby. The truck was heavily damaged. Another of the burned vehicles, a Dodge parked in the 1300 block of 29th Street, was also heavily damaged.

Less than 30 minutes after the 29th Street fires, another car was reported ablaze less than a mile away in the rear of the 1700 block of 19th Street.