DHAHRAN, SAUDI ARABIA, FEB. 18 -- Two U.S. warships, including a guided-missile cruiser, were damaged and seven crewmen injured by Iraqi mines early this morning in the northern Persian Gulf, U.S. military officials said.

The explosions marked the first time in the Persian Gulf War that ships of the multinational naval force in the waterway have struck mines laid by Iraq.

Meanwhile, allied air forces continued to pound Iraqi troops in occupied Kuwait and southern Iraq, as well as strategic targets in Baghdad, and minor ground skirmishes were reported between allied and Iraqi troops.

Although cloudy weather caused some air missions to be canceled, the allies flew 2,400 sorties during a 24-hour period ending today, bringing the total for the war to 80,000, according to Marine Brig. Gen. Richard I. Neal, the U.S. Central Command's deputy chief of operations.

U.S. officials also reported that an F-16 pilot, forced to parachute from his plane Sunday, was rescued 40 miles inside Iraqi-held territory. Neal said officials did not yet know what brought down the plane, the 21st U.S. plane lost in combat since the war began Jan. 17.

The USS Princeton, a guided-missile cruiser equipped with Tomahawk cruise missiles and the Aegis long-range air-defense system, was forced to cut its power 50 percent because of damage to one of its propellers after an explosion by an "influence" mine at 7:15 a.m. local time, the officials said.

The mine, of a type that floats underwater and does not have to come in contact with a ship but explodes in response to the sound, pressure or magnetic field caused by an approaching vessel, also put a crack in the Princeton's midsection, a military official said.

A Navy official in Washington did not disclose the full extent of damage to the ship, saying, "Any crack in your ship is certainly dangerous, but as far as the extent of interference with the ship's mission, we haven't got any definitive word."

Earlier, at 4:36 a.m., a contact mine blew a 16-by-25-foot hole in the USS Tripoli, a helicopter and troop carrier, near its bow and about 10 feet below its waterline, the official in Washington said.

The Tripoli's crew was able to seal off flooded forward compartments, but not before a diesel room, a pump room and a dry-storage locker on three different decks were flooded, according to combat pool reports that said the ship was immobile in the water for seven hours.

Central Command's Neal said both vessels remained "mission capable." The Princeton, despite having to cut its power by half, "still has all of its radars {and} missiles, so it still has all of its capabilities," Neal said.

Officials said seven crewmen aboard the two ships were injured, including a sailor aboard the Princeton who sustained serious wounds.

U.S. military spokesmen declined to say what the two ships, part of an amphibious task force of 31 warships gathered in the northern gulf, were doing at the time the mines blew up. But a combat pool filed from aboard the Tripoli reported that the ship was leading a minesweeping operation aimed at clearing a 20-mile swath off the Kuwaiti coast and strayed into what the ship's captain, Capt. Bruce McEwen, called "a very complex minefield."

The two ships were only 10 nautical miles apart.

Iraq has set adrift scores of mines in recent months in an attempt to deter an amphibious assault on Kuwait. More than 80 mines have been cleared from the gulf's waters, officers said.

In the air war, the number of sorties over the Kuwait theater of operations, which includes Iraq's Republican Guard units stationed in southern Iraq, "has been going up," Neal said.

There were 870 sorties flown today against Kuwait and 100 more directed at the Republican Guard. These bombing flights are intended to destroy Iraqi troops, cut off their supply lines and weaken their morale before any allied ground assault.

Allied ground forces, supported by Apache and other attack helicopters, continued their "aggressive patrolling, reconnaissance and counter-reconnaissance efforts all along the border" separating Saudi Arabia from Iraq and Kuwait, Neal said.

All the clashes were minor and involved artillery fire, he said. In one, Saudi and Kuwaiti forces, backed by U.S. Marine Cobra helicopters, engaged Iraqi forces with artillery and destroyed six armored personnel carriers, Neal said.

In another incident today, a soldier of the 2nd Armored Division was slightly wounded by shrapnel at about 8 a.m. when Iraqi mortar fire hit armored units in his task force, a pool report said.

And for the first time, British ground troops joined the sporadic border skirmishing. The British used remotely piloted vehicles, or drones, to locate 18 Iraqi positions in southern Kuwait and fired on them with multiple-rocket launchers, destroying three tanks, three guns and three gun positions, a British military spokesman said.

The commander of Army forces in the gulf, Lt. Gen. John J. Yeosock, was flown to Germany for surgery of an undiclosed nature, officials reported. Lt. Gen. Calvin Waller, the deputy commander of Central Command, will assume Yeosock's duties.

A U.S. military official said the Iraqi effort to protect its military sites and equipment by placing them in civilian areas is particularly widespread in Kuwait.

"He's occupied schools, religious sites, hotels," the official said, referring to Iraqi President Saddam Hussein. "Anti-aircraft emplacements are all over the hotels there. He's cleared out hospitals of equipment and put troops in there. And most of his leadership are in residential areas for just that reason: to try and protect themselves."

Staff writer Barton Gellman in Washington contributed to this report.