The growing destruction of Iraq's tank force and artillery in Kuwait means many Iraqi units have begun to disintegrate and are vulnerable to an allied ground offensive expected to include at least a corps-sized attack of 70,000 U.S. soldiers, according to senior Pentagon officials.

U.S. Army war games in California have demonstrated that when combat losses begin to approach 30 percent, units quickly lose their fighting cohesion as a result of gaps in the line, muddled communications and the psychological blow of seeing comrades killed and wounded.

The U.S. claims yesterday of 1,300 tanks, 1,100 artillery pieces and 800 armored vehicles destroyed in the first four weeks of the war represent roughly 30 percent of Iraq's armor, 35 percent of the artillery and 27 percent of the other armored vehicles located in greater Kuwait when the war began. The degradation of the 30 or so divisions composing the Iraqi army of occupation varies from unit to unit, officials said, with some -- including at least one Republican Guard division -- roughly 50 percent destroyed, while others are relatively intact.

Many U.S. officers, citing a Vietnam-inspired wariness about overclaiming enemy "kills," believe the numbers released yesterday understate the true destruction. "There's a lot of shrapnel flying around on this battlefield," a Pentagon official said, "so you're killing things and people but you're not aware of it."

The sharp increases announced yesterday reflect a recent concentration of "smart" weapons on armored targets rather than strategic sites in Iraq, as well as a refined search technique that has permitted pilots to find tanks and other targets even when they are buried and camouflaged, another senior U.S. official said.

Yet at least a small minority of intelligence analysts believe that satellite photos do not incontrovertibly support the numbers released yesterday, suggesting that the Iraqi army coiled in trenches and bunkers may still be more venomous than defanged. Independent confirmation of the numbers is impossible.

If accurate, however, the new U.S. tally of Iraq's losses shows what commanders have suggested privately for the past week: the Iraqi army is being quickly and utterly shattered. "There will be dark days ahead for us still, because {Iraqi President Saddam Hussein} is likely to use chemicals and we're going to have losses," one general said. "But there doesn't seem to be much doubt that he's going to lose his army."

The terrible pounding inflicted on the Iraqi forces, as well as the unceasing strikes against command headquarters in Baghdad and supply lines in the Tigris and Euphrates valleys, are part of a U.S. effort to "shape the battlefield." A prime tenet of the guiding American philosophy of war, known as AirLand battle doctrine, this "shaping" is an effort to reduce the enemy so that "we pit our strength against his weakness," as one top general put it this week.

Iraq's three critical weaknesses now, the general added, are "a rigid command structure that depends on top-down direction from commanders" and permits relatively little initiative by subordinates; an army that is pinned down by allied air supremacy; and a supply system whose flow has been strangled by 90 percent.

Several hundred thousand U.S. Army, Marine and allied ground troops are moving into position for the offensive that most U.S. commanders now believe is inevitable, barring Iraq's capitulation. Probing attacks and other efforts to deceive or lure entrenched Iraqi troops from their holes are likely in the near future.

But the main allied offensive -- whether launched in several days or several weeks -- will reflect U.S. doctrine of heaving overwhelming combat power against the enemy. AirLand doctrine emphasizes speed and agility; it depends on synchronization of air, naval and land forces in ways resembling intricate choreography; and it anticipates fighting at night on an almost unimaginably violent battlefield.

"We'll come with a lot of strength when we come," a senior Pentagon official said this week. "I would think you'd see at least a corps involved in the attack." The U.S. Army's tank-rich VII Corps, transferred from Europe and now poised in the Saudi desert, has about 70,000 soldiers.

The specific battle plan concocted in Saudi Arabia by Gen. H. Norman Schwarzkopf -- with help from a group of young officers known as the Jedi Knights -- is secret. But the principles used to draft that plan are discussed openly by the Pentagon and provide a blueprint for understanding the evolution of Operation Desert Storm.

For example, AirLand doctrine stresses "deep attack." This means disrupting supply lines, shattering reserve units like the Republican Guard and generally disrupting the entire Iraqi army.

In this sense, the air campaign waged for the past month is of a piece with the ground campaign that has yet to begin in earnest. Baghdad, as headquarters for the Iraqi military, is and will remain part of the battlefield. Killing a general in Baghdad is considered as useful to the allied cause as killing a general in southern Kuwait.

Cutting supply lines will pay particular dividends when the ground war begins and Iraqi demands for ammunition, food and fuel abruptly increase. An allied armored division, for instance, of 17,000 men engaged in heavy combat consumes 5,000 tons of ammunition and a half million gallons of fuel a day.

After the battlefield has been sufficiently shaped, AirLand also demands that an attacking force stress "maneuver," a quick and deceptive positioning of forces to strike the enemy.

The attack is made with a great massing of combat power, even at the risk of peeling forces away from other areas of the war zone. To minimize casualties to this juggernaut, Army planners thinking about targets have altered their standard process of "detect, decide and destroy."

Instead, "decide" is now the first element. A decision has already been made, for instance, to stress the destruction of Iraqi command and control sites, such as headquarters bunkers, in an effort to "desynchronize" the enemy. Another priority target will be Iraqi artillery, the greatest potential killer of U.S. forces with either high explosive or chemical rounds.

A number of factors remain uncertain, as is always the case in war. The killing of eight Marines by friendly fire last month has renewed commanders' concerns about large losses to "fratricide," particularly as A-10 and F-16 jet pilots try to sort out friend from foe in a close, confused night fight.

"When you look through those night sights {as a pilot} it's hard to tell which is a T-72 {tank} and which is an M-1A1. You can do that, but when you add the smoke, haze and pucker factor being up in the pilot, it becomes even more difficult," a three-star general said.

Much of the allied war planning is based on an assumption that the Iraqis will be drawn out of their deep fortifications, either by air power or to intercept a U.S. armor thrust. Because of overwhelming U.S. air power, the Iraqis have "realized that to move is to die. But if he doesn't move, it will take us longer to knock him out, tank by tank, with Hellfires {missiles} and so forth," a general said. "If he comes out of his holes and moves, the battle will be joined quicker and it will be over quicker."

As the fifth week of the war began this week, senior Pentagon officers made the following points about the progress of the fight:Iraqi "opsec," or operational security, has been surprisingly effective, in part because of a resilient fiber optic communications line running underground from Baghdad to Basra and on to Kuwait. Allied bombers have struck a number of microwave communications towers, including several in remote villages, but have had difficulty severing the fiber optic cables. As a result, the allies have had limited success in forcing Iraqi commanders "up into the air" -- giving orders by radio -- where such communications are vulnerable to U.S. eavesdropping. Allied aircraft losses of roughly one every 3,000 sorties have been one-quarter of the loss rate suffered by the United States in Vietnam for eight years. Three days before the war started, the Air Force told President Bush to expect five U.S. Air Force losses a day, and 150 planes lost over the course of a four-week bombing campaign. Instead the Air Force, which is flying 70 percent of all allied sorties, lost only a handful of planes in the first month of combat. It took allied bombers more than three weeks to knock out just 17 major bridges, particularly because in the first week relatively few smart munitions were diverted from strategic targets to the task. Many Navy "dumb" bombs dropped by F/A-18 and A-6 bombers flying from the Persian Gulf to the Basra area missed their targets, a senior Pentagon official said, and as a result supplies continued to pour into Kuwait until early this month. Given the Iraqi entrenchment, U.S. targeteers have used an estimated "kill ratio" of two attack sorties per vehicle, an official said. A typical Iraqi division may have 350 tanks and 350 armored personnel carriers, which in theory means that 140 sorties are needed to decimate the division and 1,400 to obliterate it.

The relatively low number of Iraqi defectors thus far has surprised U.S. military planners, who sent hundreds of military policemen to Saudi Arabia in expectation that thousands of "line crossers" would flock to the allies. One senior official said it is still unclear whether this hesitancy is because of Iraqi loyalty or because would-be defectors are afraid to brave their own minefields and execution squads.

Staff writer George C. Wilson and staff researcher Lucy Shackelford contributed to this report.