Coalition forces entered Diwaniyah, going a couple of blocks inside the town, where local residents told translators where to find the Baath Party headquarters and the military headquarters from which rocket-propelled grenades had been fired, said Capt. Brian Lewis of the 1st Tank Battalion. 

Marines fired on both buildings, and on a military compound in a date palm grove outside the town. Lewis, of Richmond, Wash., said 80 to 90 Iraqis were killed in fighting in Diwaniyah. 

The coalition forces also found a large ammunition dump Monday that included 41 buildings and about 6,000 mines, stacked like checkers. Lewis said there was a whole building of rocket-propelled grenades stacked floor to ceiling. It was crammed full of ammunition. It was too big to blow up, forcing an engineering unit to mull over how to dispose of it. 

Elsewhere, American warplanes also hammered defensive positions south of Baghdad overnight and dropped bombs on an Iraqi presidential yacht and another ship in the southern port of Basra, Navy officials said. 

U.S. warplanes had bombed the yacht, Al Mansur, a week ago, but it didn't sink, said Lt. Cmdr. Mike Brown, a spokesman for the Kitty Hawk carrier battle group. 

The ship was hit again with laser-guided bombs, but Brown said Kitty Hawk officials couldn't confirm if the boat was now sunk. However, Capt. Thomas A. Parker, the Kitty Hawk's commander, said the yacht and the other ship in Basra's port "were burning when they (the planes) left." 

A Patriot missile battery destroyed a missile fired from south of Baghdad at U.S. forces in central Iraq, said Capt. Pat Costello of the 101st Airborne Division. A chemical alarm detector was set up to check whether any chemical weapons were used, but an official determination was not immediately made. 

An Iraqi missile was also shot down by a Patriot missile battery before it reached Kuwait, the military said. 

A Marine intelligence analyst said coalition forces had flown 18,000 sorties and cut back the Republican Guard by 50 percent. The analyst said there was heavy bombing Tuesday of Kut in southeastern Iraq to clear the way for ground forces. 

Marine ground forces also have secured an airbase at Qalat Sukkar, southeast of Kut, that is expected to serve as a staging ground. 

Around Diwaniyah, 75 miles southeast of Baghdad, Marines came under fire from artillery and mortars. Hundreds of Iraqi fighters with rocket-propelled grenades and rifles were said to be inside the town. 

Marine 155mm howitzers miles away opened fire on Iraqi mortar positions, tanks and bunkers. 

There were no reports of Marine casualties. 

At least three Iraqis were wounded: two very thin Iraqi soldiers who had been shot in the legs and were being treated with their hands bound behind their backs with silver duct tape; and an older man who had been shot in the back and leg. 

Diwaniyah is along one of three main south-north routes U.S. forces are using to get to Baghdad. The Marines have been coming under rocket fire so it was important to clear the area and force attackers back. 

Overnight, warplanes struck at Iraqi positions around Karbala and Hindiyah, about 50 miles short of Baghdad, in a U.S. effort to open the way for the invasion of Baghdad by American forces massing outside the city. 

U.S. troops in the desert watched B-52s circle and drop bombs near Karbala Tuesday afternoon, and as the sun set, dozens of cruise missiles left contrails as they flew overhead, heading toward Baghdad and Karbala. 

"It's nice to look up and know that everything up there is friendly," said 1st Lt. Eric Hooper of Albany, Ga. "It makes you feel a little better about rolling up that way." 

The bombing was in support of the Army's V Corps and hit surface-to-air missile sites and a bridge across the Euphrates River, said Lt. j.g. Nicole Kratzer, a spokeswoman for the air wing of the aircraft carrier USS Kitty Hawk. 

On Monday, Army forces fought pitched battles at the Euphrates River town of Hindiyah against Republican Guards and other Iraqi loyalists. 

After the battle, soldiers from A Company, 3rd Battalion, 7th Infantry Regiment rested Tuesday, cleaning their weapons, listening to music and relaxing. 

Lt. Col. Philip DeCamp, the battalion commander, said the troops should not assume that all battles would go as smoothly as Monday's fight in Hindiyah. 

"We need to keep these guys from becoming complacent, thinking they can take anything the Iraqis throw at us," he said. DeCamp warned that the defenders south of Baghdad will have more powerful weapons, capable of penetrating the armor on U.S. vehicles.