Iraqi armored forces charged out of occupied Kuwait and battled allied forces in Saudi Arabia throughout the day Wednesday, killing 12 U.S. Marines in the heaviest ground fighting of the Persian Gulf war. The Pentagon said the enemy was stopped and suffered heavy losses.

Iraqi tanks and other armored vehicles, which had been massing inside Kuwait near the Saudi border, rumbled over the frontier in four separate places about midnight local time (2 p.m. MST Tuesday), some heading to the Saudi oil town of Khafji, where they were met by allied ground forces, including U.S. Marines, according to staff officers of the 1st Marine Division.The Pentagon estimated the size of the Iraqi force at about 1,500 soldiers; the number of allied soldiers involved in the battle was not disclosed.

The charge on Khafji, which was abandoned by its residents on the first day of Operation Desert Storm, was followed by hours of heavy ground and air fighting described by Marine Lt. Col. Cliff Myers as "hellacious."

Twelve U.S. Marines were killed in the battle, Gen. H. Norman Schwarzkopf, the U.S. commander of the allied forces, said at a news briefing in Riyadh, the Saudi capital. A Saudi military spokesman said his nation's troops also suffered casualties but they were "very limited."

The Pentagon said about one-third of the Iraqi force was injured or "otherwise incapacitated" and suffered heavy equipment losses.

There were conflicting accounts from the Pentagon on whether the Iraqi forces had been driven back. At first a Pentagon official said they were "repelled," but later he acknowledged that it was unclear whether Iraqi troops were still in Khafji, and he emphasized that it would be too strong to say the enemy force had been "defeated."

In Riyadh, U.S. Central Commandspokesman Lt. Col. Greg Pepin said the engagement was an "ongoing operation" late Wednesday. Pool reports from the battle area said Saudi and Qatari troops were fighting the Iraqi forces in Khafji as late as 1 p.m. local time (3 a.m. MST), at least 13 hours after the initial advance, with U.S. Marine artillery support.

The Marine staff officers in Saudi Arabia said at least 20 Iraqi Soviet-made T-55 tanks and armored vehicles were destroyed and 13 enemy soldiers were captured in the border battle.

The Marine officers said Iraqi forces also were hit by U.S. Air Force A-10 Warthog anti-tank aircraft, Marine A-6 fighter bombers and Marine AH-1 Cobra helicopters.

It was clearly the heaviest ground fighting since the U.S.-led multinational force began air strikes on Iraq and occupied Kuwait on Jan. 17. Previous ground action has involved skirmishes with negligible casualties.

But in Washington, White House spokesman Marlin Fitzwater emphasized that the battle did not mean that the allies had begun their ground offensive aimed at driving Iraqi troops from Kuwait. "The incursion did not represent the start of the ground war, no," he said. "We have not done that."

Fitzwater also said President Bush was "very saddened" by the casualty report.

Asked why allied troops did not bomb the Iraqi forces as they were massing in Kuwait just before the advance on Khafji, a senior Pentagon officer said he believed that they may have wanted to let the enemy cross into Saudi Arabia for a fight in the open, where the Iraqis might be more vulnerable.

A Pentagon official called the Iraqi charge a "probing attack," saying it would be an "overstatement" to call it a major offensive signaling the start of a ground war. "It's not really designed to capture ground," he said, but to "feel the enemy line out."

Meanwhile, a total of about 90 Iraqi planes had reached Iran as of Tuesday, Pentagon officials said, but restated their belief that the unexplained exodus did not pose a threat. About 65 percent of the aircraft were said to be fighters and bombers and the rest are military and civil and military transport planes.

An allied military spokesman in Riyadh said the allies Wednesday conducted more than 3,000 air sorties against Iraqi positions, bringing the total number of missions in two weeks of war to more than 30,000.

In other fighting Wednesday, Lynx helicopters from British destroyers in the northern Persian Gulf attacked and sank three Iraqi patrol boats, the British Broadcasting Corp. reported. Five Iraqi boats were sunk Tuesday by U.S. Intruder bombers and the Lynx helicopters.

Meanwhile, the 20-by-60-mile oil slick continued to creep southeast through the Persian Gulf, but no more crude is feeding the spill.

The slick appeared to be breaking up, an official said.