A massive aerial assault by volleys of cruise missiles and precision-guided bombs followed by sharp ground attacks -- some deep inside Iraq -- would mark the opening days of the war against Iraq.

The goal is to deliver such a stunning blow against Saddam Hussein's forces that resistance will collapse before American-led troops reach the capital, Baghdad, where the Iraqi regime is believed to be planning its most vigorous defense.

Gen. Richard Myers, chairman of the Joint Chiefs of Staff, says the idea is to create "such a shock on the system that the Iraqi regime would have to assume early on that the end is inevitable."

That would be a different type of campaign from the 1991 Gulf War, when weeks of air attacks preceded what was only a 100-day ground war. This time, the U.S. military is likely to be testing "swarm" tactics -- launching near simultaneous offensives by air, ground and special forces, leaving a confused, overwhelmed enemy without a clear front line to defend.

A key test will come in the opening days, when U.S. and allied military planners learn what portion of Saddam's forces has survived. If enough remains intact to defend Baghdad, U.S. troops could face bloody, house-to-house fighting in a city of 5 million people.

American troops here in Kuwait have been training for months in techniques of urban warfare.

In Iraq, meanwhile, soldiers, civilians and Baath Party members have been digging trenches and sandbagging government buildings.

On Saturday, Saddam reorganized the country into four military zones commanded by his son Qusai and three trusted lieutenants. The move appeared aimed at enabling regional commanders to take decisions without waiting for orders from Baghdad.

Gen. Tommy Franks, the head of Central Command, has assembled about 280,000 troops, including 30,000 from Britain. Most are stationed in Kuwait, the main launch pad for a ground invasion.

That force is less than half the 30-nation coalition that drove Iraqi forces from Kuwait in 1991, and smaller than the four to five heavy divisions that planners had once sought for the war.

The main Army forces are the 3rd Infantry Division and the 101st Airborne Division, the Army's only helicopter assault division, both in Kuwait.

With more than 200 tanks, the 3rd Infantry is expected to spearhead the drive to Baghdad. In a sign that soldiers of the "Iron Fist" division have moved to the brink of battle, troops of A Company, 3rd Battalion, 7th Infantry Regiment, were issued their "basic loads" of live ammunition on Monday. They were told to break camp and be ready to move into action on a moment's notice.

Also assembled in northern Kuwait are more than 50,000 U.S. Marines. Some are expected to take part in a dash up the western flank of the Tigris-Euphrates Delta toward Baghdad, while others would join British forces to capture the southern city of Basra and the strategic Shatt al-Arab waterway, Iraq's outlet to the Persian Gulf.

If the Iraqi defense doesn't crumble swiftly, the war could last weeks and pose grave risks for U.S. troops. One perilous possibility is Saddam launching a pre-emptive chemical or biological attack on allied forces.

However, Iraqi army morale is believed to be low and if serious resistance is mounted, it is expected to come from the estimated 80,000-strong Republican Guard, which Saddam is expected to deploy in the area around Baghdad and his hometown of Tikrit to draw allied troops into street fighting.

To prevent that, air power is key. Allied planners have assembled a formidable array of more than 1,000 U.S. and British warplanes. Analysts have said they expect as many as 3,000 precision-guided bombs and missiles to be launched in the first 48 hours.

The first planes to penetrate Iraqi airspace may be the Air Force's radar-evading stealth jets -- the F-117B Nighthawk fighter, which led the attacks on Baghdad in the 1991 Gulf War, and the bat-winged B-2 bombers.

At about the same time, some 30 Navy ships and submarines in the Gulf and Red Sea would launch hundreds of satellite-guided Tomahawk cruise missiles at targets in Baghdad and elsewhere.

"It will be designed to paralyze enemy forces rather than destroy them," Anthony Cordesman, a leading expert on Iraq and U.S. military power, wrote in an analysis March 15. Once the war begins, Cordesman predicted, the Iraqi regime "will be gone in days or weeks."

Another key element would be Navy F/A-18 Hornets and F-14 Tomcats flying from five aircraft carriers in the Persian Gulf and eastern Mediterranean. Each carries about 50 strike planes.

The Air Force's fighters and bombers would launch from bases around the Gulf, plus the Indian Ocean island of Diego Garcia. Some might even come from Europe. The Marine Corps has dozens of F/A-18 fighters, AV-8B Harrier jets and AH-1 Cobra attack helicopters.

The U.S. strategy is predicated on speed -- not just in getting ground forces to Baghdad, but also in communications enabling pilots, for example, to switch target coordinates in mid-flight.

The ground assault is designed to be a lightning movement similar to the opening of the Gulf War, with M1A1 Abrams tanks, mine-clearing vehicles and other armored forces blasting through dirt ramparts and across oil-filled trenches on portable bridges laid by combat engineers.

Close air support would come from Army AH-64 Apache attack helicopters and Marine Corps Harrier jets, among others. "We've been practicing `the dance' -- the battle rhythm," said "Scott," the commander of a Harrier squadron based on an assault ship offshore.

The main axis of attack is expected to involve the Army's 3rd Infantry Division and 1st Marine Division, striking northward on the western side of the Tigris-Euphrates Delta toward Baghdad.

Cordesman and others say that despite years of intermittent U.S. and British bombing of Iraq's air defenses in the southern and northern "no fly " zones, Iraqi retains formidable batteries around Baghdad. These include surface-to-air missiles that seriously threaten allied pilots, even at night.

Most analysts say Iraqi ground forces are far weaker since losing huge numbers of tanks and artillery pieces in the Gulf War and lacking spare parts for those that remain.

Saddam's wild card could be chemical and biological weapons; he claims he has none, but U.S. commanders believe he does and may use them if his survival is at stake. U.S. and British troops have trained for weeks in how to fight during a chemical attack.

In addition to attempting to neutralize Iraq's air defenses, the air campaign would target key communications "nodes," while generally avoiding civilian infrastructure like bridges and power stations.

Also to be targeted early are the H-3 airfields in far western Iraq where Saddam may have Scud missiles. Some believe U.S. and British special operations forces would secure these sites. Likewise, the oil fields in northern and southern Iraq need to be secured.

Franks' original plan to base the 4th Infantry Division in Turkey to open a northern front was thwarted when the Turkish government refused to allow access to its bases. Turkey agreed Monday to reconsider, but the approval may come too late for the division to take part in the initial fighting.

So allied planners have to find other ways of subduing Iraqi forces in the north and seizing control of the oil fields to prevent Saddam from destroying them in a scorched-earth defense.

The most likely approach is a helicopter-borne assault into the north by the 101st Airborne, one of the trickiest aspects of Franks' war plan.

U.S. special operators -- commando-type forces -- reportedly already have been securing landing strips in northern Iraq.

Another possibility for action in northern Iraq is the 82nd Airborne Division. "Our mission is to jump in denied terrain. We'd be the candidates for that," said Capt. Paul Jackson, commander of a 105mm howitzer battery in the 82nd's 2nd Brigade.