A U.S. Navy frigate opened fire on a suspected Iranian patrol boat when the craft began "an apparently hostile run" toward an American military supply ship in the southern Persian Gulf Sunday, Defense Department officials said yesterday.

The patrol boat, believed to be a Boston whaler-type speedboat, fled along with two other suspected Iranian vessels, after the frigate USS Carr fired machine gun rounds at the craft, according to Pentagon officials. Officials said they do not know if any of the bullets struck the speedboat, but said the boats did not return fire and no Americans were injured.

Defense Secretary Caspar W. Weinberger described the incident as "part of the normal" tensions in the Persian Gulf region. It is the fourth time U.S. forces have fired on Iranian boats, aircraft or military installations since the United States began escorting reflagged Kuwaiti tankers through the gulf in July.

The incident occurred as the Carr was escorting the motor vessel Patriot, a supply ship chartered by the Military Sealift Command, in the southern gulf near the Strait of Hormuz about 10:30 a.m. EST Sunday, officials said.

Pentagon officials said a suspected Iranian dhow and two Boston whaler-type craft approached the Patriot "at high speed."

The crew of the Carr was ordered to general quarters and attempted unsuccessfully to contact the three boats by radio, then fired warning shots, officials said.

When the boats did not change course and moved within 500 yards of the American ship, the Carr opened fire on the lead boat with .50 caliber machine guns, according to Pentagon officals.

"They stopped and turned tail and ran," Weinberger told reporters in California where he is participating in the semi-annual NATO Nuclear Planning Group meeting.

Pentagon officials said the U.S. frigate and the supply ships continued their trip out of the gulf after the incident. The supply vessel is one of several such ships that visit the gulf each month to replenish supplies and equipment for American forces.