The United States would win a war against Iraq in under three months, according to the latest secret Pentagon estimates. That is not simple bravado by overconfident brass. Casualty estimates in the tens of thousands have been enough to dampen any Rambo spirit at the Pentagon. The projections for a quick and dirty victory come from cold facts.

The United States has superior air power in the region - more than 1,000 combat aircraft. The Iraqis have 500, the best of which are about 100 French Mirage fighters armed with Exocet missiles that are useful against large, slow-moving or stationary targets. Iraqi pilots are no match for their American counterparts, and they have never been tested in war. Iraq fielded no air force to speak of during its 8-year war with Iran.Superior air-to-air missiles also give America the advantage. The Sidewinder, the Sparrow and the Phoenix missiles can be shot from any angle at other aircraft. The current war plan favors a massive air assault in the opening hours of the conflict. American, British and Saudi Arabian jets would be sent in first to knock out Iraqi anti-aircraft batteries, radar systems and airfields. Then the slower bombers would follow, making possibly as many as 3,000 bombing runs a day, to knock out nuclear, chemical and biological weapons sites, command centers and munitions factories.

Iraq is banking on its tanks - 5,000 in all, with 3,500 of them now waiting for action in Kuwait and southern Iraq. The best is the Soviet T-72, which first rolled off the assembly line 17 years ago. The next best is the even-older T-62 that can only shoot while standing still and then has only a 50-50 chance of hitting its mark. Most of the huge tank force is terribly outdated and inferior. The United States has more than 1,000 tanks in the region including the top-of-the-line M-1 Abrams, first fielded in 1987. It shoots on the move, is extremely accurate, has a range of two miles and can fire every few seconds. Iraq has no navy, and that was OK as long as it had only a small coastline to protect. But now it must defend the coastline of Kuwait and vulnerable islands in the Persian Gulf. About 125,000 Iraqi troops are assigned to the coastal defense where they face a massive armada of five aircraft carriers and 11,000 Marine amphibious assault troops.

If the United States goes to war, it likely would attack from three fronts. The prime attack would come from Saudi Arabia to the south and the Gulf to the east. The United States has received hints from Turkey that the Turks may allow an assault from their country to the north with the help of nearly 100,000 Turkish soldiers already on the border. The United States doesn't have the fourth front - the west - covered, because it belongs to Jordan, and King Hussein has allied himself with Saddam Hussein. The United States is still hoping that the little king will see the light.

The Iraqis are tenacious but sluggish fighters. The Iran-Iraq war dragged on over most of a decade simply because both sides dug themselves in and didn't move much. Iraq has not faced the kind of mobile offense that America and its allies have in mind. Nor can they last long without spare parts that have been held back by the embargo. The bottom line at the Pentagon is that while Iraq will claim thousands of U.S. lives, it will not win.