Military commanders have told U.S. troops that more than half of those attacking Iraqi desert trenches could be killed or wounded, a newspaper reported Friday.

American troops in Saudi Arabia and California have practiced attacks against replicas of Iraqi fortifications based on satellite photographs, and the projected casualties were heavy, the Los Angeles Times said.Marine Corps commanders recently told troops that results from about 180 mock battles show casualties in the ground attacks can exceed 50 percent, the newspaper said.

In another exercise, an Army unit of nearly 2,000 men was ordered to break through a "triangular strongpoint" occupied by a smaller unit, and one-third of the American troops would have been killed or wounded, the Times said.

However, military experts said the U.S. military is unlikely to launch massive direct assaults on land. Aerial and artillery attacks, followed by flanking movements, are more likely, they said.

Still, some commanders said land attacks likely will be important because Saddam Hussein's army has had five months to dig itself in against air raids.

Some estimate that 270,000 Iraqi soldiers are entrenched along the full length of the Kuwaiti border and about 100 miles into Iraq.

"Anything that has been deliberately constructed over months is going to pose real problems," said Capt. Ralph Corradi, operations officer of a combat engineer battalion in the Army's 24th Mechanized Division.

Among the expected Iraqi fortifications are trenches filled with burning oil, something U.S. troops have not encountered before.

The so-called flare pits have so far defied conventional solutions, although military engineers are experimenting with explosives aimed at collapsing the pits, the newspaper said.