DHAHRAN, SAUDI ARABIA, JAN. 27 -- U.S. fighter-bombers and warships in the Persian Gulf are engaged in what one senior military official calls "a deadly game of hide-and-seek" with Iraqi patrol boats, many believed to be carrying powerful anti-ship missiles, that pose a threat to allied vessels.

U.S. military officials have expressed particular concern about Iraq's arsenal of French-made Exocet missiles, which can be fired from aircraft or vessels. The anxiety over the Exocet was heightened last week when a Saudi F-15 fighter pilot shot down two of Iraq's French-built Mirage F-1 fighter-bombers loaded with the missiles.

The U.S. Navy already has experienced the damage that an Exocet can cause to its thin-skinned ships: In May 1987, an Iraqi pilot fired two Exocets into the hull of the USS Stark, a guided missile frigate on patrol in the Persian Gulf, killing 37 men. Iraq said at the time that the missiles were fired accidentally.

U.S. intelligence officials said they believe Iraq also has armed many small, civilian boats with antiaircraft missiles.

Although U.S. military officials have scoffed previously at the small Iraqi navy, which is thought to have only about 50 ships and small vessels, Navy officers say they could be more troublesome than anticipated. "The patrol craft tend to introduce an element of lack of complete control over the sea. There is no question we have got to take them out," said Capt. Ernest E. Christensen, of the aircraft carrier USS Ranger.

While the three American aircraft carriers in the gulf have launched waves of bombers at Iraq's largest naval yards, pilots and Navy officials say bad weather has prevented them from determining exactly how many vessels have been sunk. But today, Army Gen. H. Norman Schwarzkopf, commander of the allied forces in the gulf, put the known total of sunken or badly damaged Iraqi vessels at 18.

Radar in U.S. surveillance aircraft, normally highly effective against sea targets, has been confused by the many oil platforms that dot the northern Persian Gulf and create blips on radar screens. Elusive Iraqi patrol boasts attempt to use that to their advantage, seeking refuge amid the tangle of platforms.

"I think that you are going to see a deadly game of hide-and-seek," said Capt. Marc Liebman, who helps operate the Ranger battle group's tactical information center. "The Iraqis are not as aggressive as we had thought, but they are not as easy to find as we had thought either."

Pilots are also impeded in their search for the small Iraqi vessels by clouds, fog and identification problems. Some Iraqi patrol boats are identical to those from allied nations, including Kuwait. Some pilots say they can verify that a vessel is Iraqi only after it fires at them.

Telling the difference between friend and foe is a continuing problem in a war in which many nations in the coalition opposing Iraq fly the same kinds of planes as the Iraqi air force and enemy and friendly sea-going vessels also can be easily confused. Allied rules of engagement require that pilots make positive visual identification of planes and ships before firing at them, rather than relying solely on electronic identification systems.

In the skies above the battlefield, one of the deadliest dogfights in the 11-day-old war unfolded today when two U.S. F-15 fighter pilots shot down four of Iraq's Soviet-built MiG-23 jet fighters.

Allied forces have so far lost no aircraft in air-to-air combat, and no allied planes have been downed by ground fire in the last two days, Schwarzkopf said.

At the same time, Schwarzkopf reported that at least 39 Iraqi aircraft -- including some of Baghdad's best fighter planes -- have fled to neighboring Iran in recent days, 23 of them in a 24-hour period ending at 7 p.m. (11 a.m. EST) today.

The general said he had no idea why the Iraqis were flying to Iran, which waged war against Iraq between 1980 and 1988 but has remained officially neutral in the Persian Gulf War. "It may be that they have decided they can't afford to lose any more aircraft . . . but that is purely speculation," the general offered. He said he would take Iran "at its word" that any planes from either side landing on its territory would be forced to remain there until the end of the conflict.

As clouds continued to frustrate allied efforts to assess damages to the Iraqi military after about 22,000 aerial missions, about half of them involving bombing raids and half support missions, the British Royal Air Force sent Tornado GR-1 jets equipped with infrared sensors streaking under the dense cloud cover Saturday night to collect images of destruction on the ground. The planes returned with a variety of information, including evidence that bridges attacked by U.S. bombers earlier in the day were ablaze, according to British military authorities.

British officials also said their warplanes destroyed an Iraqi missile site, equipped with Chinese-built Silkworm missiles, that threatened allied ships and potential amphibious operations. However, U.S. naval authorities said they are still attempting to discern whether Silkworm sites they have bombed are actual missile launching facilities or dummy sites.

Schwarzkopf also said allied forces destroyed three Scud ballistic missile launchers Saturday night. But he added: "It's very difficult to confirm that sort of thing. It's a very small target and a mobile target. The only time I'm going to be satisfied is when no more are fired."

In response to Iraqi claims that the allies have been indiscriminately bombing residential neighborhoods and nonmilitary industries, Schwarzkopf said allied pilots are taking exceptional measures to avoid civilian casualties. "We are absolutely doing more than we ever have -- and I think any nation has -- in the history of warfare, to use our technology" to avoid civilian damage, he said.

Furthermore, he said, "by following this course of action" the United States might be endangering the lives of its pilots. But, he added, in warfare accidental bombings of civilian areas are "going to happen, no question about it."

U.S. officials continued to report scattered defections by Iraqi troops. A Navy A-6 Intruder bomber pilot flying over the tiny Iraqi-held island of Maridum, just off Kuwait, noticed a message spelled -- actually misspelled -- in stones on the beach below him: "SOS We Serrender."

Cmdr. Mark Lawrence, intelligence officer for the aircraft carrier USS Theodore Roosevelt, said officials believe Iraq had dispatched 20 to 30 troops to the island to warn their forces of incoming allied aircraft but had been unable to resupply the island for at least a week.

"We will probably go and pick those guys up," said Lawrence.

U.S. forces in the desert near the Saudi-Kuwaiti border said they are greeted almost every morning by a handful of Iraqi soldiers waving white T-shirts, most saying they have not eaten in two or three days, officials said. Allied forces are now holding more than 110 Iraqi prisoners of war.