No connection has been found between three major fires that occurred within 24 hours along a five-mile commercial strip in Gaithersburg and Rockville, a Montgomery County fire official said yesterday.

Fire officials believe that the third blaze, which was reported at 8:28 p.m. Saturday in a vacant building in the 100 block of North Frederick Avenue in Gaithersburg, was arson, said department spokeswoman Angela Withers.

The causes of the two earlier fires have not been determined, she said. Together, the fires caused more than $1 million in damage.

Firefighters were called to the first fire, in the 400 block of North Frederick Avenue, about 1 a.m. Saturday. The blaze started in a dry cleaners in the Gaithersburg Square shopping center and spread to three other businesses before it was extinguished.

The damaged shops included a Reliable Home Appliance store, a Super Fresh market and Kim's Hunan Restaurant. The Super Fresh market opened yesterday, but the two other businesses remained closed.

The second fire occurred about two hours later in the 16000 block of Frederick Road in Rockville. The fire caused extensive damage to a two-story Public Storage facility.

It took about 2 1/2 hours to extinguish the third blaze. One firefighter sprained his shoulder in the incident. He was treated at a hospital and released early yesterday.