Arlington County fire officials and agents from the federal Bureau of Alcohol, Tobacco and Firearms said they suspect arson in the explosion and three-alarm fire that gutted two stores and damaged a third early yesterday in Crystal City.

Arlington Fire Chief Thomas M. Hawkins, who estimated the damages at $300,000, said the department normally asks the federal agency for assistance whenever a fire is believed to be caused by an explosion.

Neighbors who live near the one-story shopping center in the 2900 block of South Eads Street called firefighters about 2:30 a.m. yesterday, shortly after they reported hearing an explosion.

Hawkins said two 5-gallon gasoline tanks found in the rear of the stores were being tested to determine if they were involved in the blast.

He said he doubted there was a connection between the explosion and the fact that one of the stores, George's Spanish-American Grocery, is owned by an avowed admirer of the Palestine Liberation Organization. "We can't say yet what's the most accurate theory" behind the explosion, he said.

George Barbari, the grocery store owner, said he is a Palestinian from Jerusalem who has lived in this country 16 years. "I support the PLO , that's all," he said. "I'm proud of what I am and I like to advertise it . . . . But the PLO support has got nothing to do with this," he said, standing near his truck bearing Virginia license tags "PLO 1."

Terry Lunders, ATF supervisor on the scene yesterday, declined to offer any theories.

"Many things are possible," he said.

In addition to the grocery store, the explosion and fire gutted Moro's Pizzeria. The TNT T-shirt and Transfer store, also in the center, was damaged by smoke and water, fire officials said.