Five families were left homeless temporarily yesterday afternoon after a two-alarm fire caused about $300,000 damage to six renovated row houses in Old Town Alexandria, Alexandria fire officials said. No one was injured in the blaze, which took firemen about 5 hours to extinguish.

Fire officials said they believe the fire started in the basement of the row house at 531 S. Fairfax St. then shot apward through an open wall space to the attic. The blaze then spread quickly to five other adjoining three- and four-story row houses, all of which shared a common attic.

The damaged houses, numbering from 529 to 539 South Fairfax, are five blocks from the Old Town commercial district.

Fire officials said they were hampered by heavy snow and sub-freezing temperatures that froze their breathing apparatus as they fought through heavy smoke in the wood frame houses, which ranged in value from $100,000 to $175,000.

Mark Edes, owner of number 529, the most heavily damaged of the buildings, said he had bought the house four weeks ago and was planning to move in after completing renovation of the 80-year-old building in April.

"We were looking forward to removing the last eyesore in the neighborhood. We never thought it would be removed this way," he said.

Four of the houses were identical 12-foot-wide bayfronts built early in the century for the shipbuilding industry on the Alexandria waterfront. All of them but Edes' had been restored since 1970. The least damaged of the homes, number 539, originally was a corner store during the Civil War.

Frank Ross, a treasury department lawyer, who rented number 535, watched firefighters try to save his house from the leaping flames, saying ruefully, that "a fire like this is something you are aware can occur but you think it will never happen to you."

Cause of the fire was still under investigation last night.