One year after the USS Stark was attacked by a "friendly" Iraqi jet fighter, American ships in the Persian Gulf continue to operate under war-time rules of engagement designed to prevent a repetition of that tragedy.

The ground rules for fighting have been modified several times since the Stark was attacked on May 17, 1987, primarily to expand the number of situations in which American warships may come to the aid of merchant ships.But the first change to the rules made by the Pentagon after the attack, which killed 37 seamen, was to authorize ship commanders to open fire on any plane or vessel that came close enough to fire on their ship - and those guidelines remain in place.

"There are really two U.S. navies - one for peace and one for war," Dr. Michael Vlahos, the director of the State Department's Center for the Study of Foreign Affairs, observed recently. "The difference is mental readiness.

"In war, one's senses are honed for battle; in peace, even where the threat of `inadvertent attack' is considered, one's senses must be leashed," Vlahos said.

That peacetime leashing may have left the Stark's crew "mentally disarmed," Vlahos argues.

The Stark's crew knew for an hour that a jet fighter was flying in their direction and that it was "assumed friendly, assumed Iraqi."

No effort was made to warn the plane away until it was too late. The fighter fired two Exocet missiles, 30 seconds apart. The first was a dud. The second nearly sank the ship.

One year later, the Stark sits dockside at Ingalls Shipbuilding in Pascagoula, Miss., receiving the finishing touches of an overhaul that will cost an estimated $100 million. The careers of two of her officers - including the skipper - have come to a forced end.

Iraq has acknowledged its fighter pilot mistakenly fired on the Stark - thinking it was a tanker carrying oil for archenemy Iran. Iraq has pledged to make restitution, although no money has changed hands and probably won't for years.

More than two dozen U.S. Navy ships now operate in and around the gulf, escorting U.S. tankers as well as 11 Kuwaiti oil tankers reregistered to fly the American flag. The convoy work began despite congressional opposition spawned by the Stark incident.

U.S. ships also are now cleared to come to the aid of neutral merchant vessels in certain circumstances. Four different battles have been fought with Iranian forces. And the administration is vowing to protect the right of freedom of navigation indefinitely.

The Navy, meantime, long ago came to the conclusion the ship's officers should have prevented the Stark tragedy. Noting that "no ordnance was fired in defense of Stark or in retaliation for the attack," a board of inquiry concluded:

"The rules of engagement that existed on May 17, 1987, were sufficient to enable Stark to properly warn the Iraqi aircraft . . . and if the warning was not heeded . . . to defend herself against hostile intent and imminent danger without absorbing the first hit."

The ship's commander, Capt. Glenn R. Brindel, "failed to provide combat-oriented leadership, allowing Stark's anti-air warfare readiness to disintegrate to the point that his Combat Information Center team was unable to defend the ship," the board added.