A fire of undetermined origin early yesterday caused extensive damage to the interior of the Crandall Building at 405 7th St. NW, one of a group of vacant, store-front buildings recently purchased by the Pennsylvania Avenue Development Corp. to save their architecturally significant facades.

Although the fire heavily damaged the interior of the building, which formerly housed the Marc Anthony clothing store, PADC officials said it would not affect plans to preserve the front of the structure. The building, a block and a half borth of Pennsylvania Avenue, is in an area slated for commercial and residential redevelopment.

The fire broke out about 7 a.m. according to D.C. fire officials, who reported that most of the damage occurred on the top floor of the four-story building. The cause of the fire is under investigation.

The PADC bought the row of rundown, vacant buildings in February for $913,000 from the Seventh Street Limited Partnership, a real estate firm in which developer Dominic F. Antonelli Jr. is a major partner.

PADC paid almost twice the assessed value for the buildings, according to listings in the 1977 Luck's Real Estate Directory. The plan is to retain the fronts of the buildings with new development behind them, a spokeswoman for the redevelopment agency has said.

The Seventh Street Partnership had wanted to demolish the buildings for a parking lot after the buildings were vacated, according to PADC officials. But the PADC blocked the demolition plan and then decided to buy the buildings.

According to a PADC report on buildings in the Pennsylvania Avenue area, the row is "one of the finest expressions of late 19th Century commercial architecture in the area." The Crandall Building was built in 1887. In recent years, businesses in the 7th Street area that includes the Crandall building have been adversely affected by subway construction.

Among the firefighters responding to the scene of the two-alarm fire was Beatrice Rudder, the city's first woman firefighter, who reported to work earlier this week after she graduated from the fire academy.