Fire investigators said yesterday that the $1.5 million fire which destroyed a military exchange store on the Army's Cameron Station in Alexandria had suspicious origins.

Col. Richard S. Briggs, Cameron's post commander, said that blaze apparently started outside of the base's "Four Seasons" store about 10:46 p.m. Friday. The 39-year-old, 40-by-80 foot, wood structure "went up like kindling," said one firefighter.

It took nine firefighting squads from Alexandria and Fairfax County three hours to bring the fire under control, said officials. Icy conditions and explosions from propane, kerosene and aerosol paint containers inside the store made fighting the fire difficult, said an Alexandria official.

Army officials said the building, which was to be demolished for a new facility, contained beverages, toys, hardware, and lawn and garden supplies sold through the military exchange system.

Two Alexandria firefighters sustained minor injuries that did not require hospitilization, said dispatchers.

Although investigators said yesterday that they had not determined what started the blaze, they said they believed it had suspicious origins. Cameron Station, located off Duke Street in the western section of Alexandria, has no housing and is surrounded by fences and patroled by security personnel with guard dogs.