American troops engaged in fierce ground combat with Iraqi soldiers and militiamen across a 150-mile swath of central and southern Iraq to protect supply lines, soften defensive positions and eliminate rear-guard resistance.

Ground troops mounted operations in and around at least four key cities -- Nasiriyah, Samawah, Najaf and Karbala -- to flush out Iraqi regular army units and paramilitary groups. At the same time, coalition warplanes and cruise missiles bombarded Baghdad, hitting a presidential palace and a training center for paramilitary forces.

Units of the 3rd Infantry Division pushed north to the outskirts of Karbala after overnight air strikes largely decimated three Iraqi army mechanized and tank units guarding the city. Nightly air strikes in recent days have destroyed much of Baghdad's air defenses but have done less to inflict the damage on the Republican Guard divisions defending the capital that ground commanders want.

Gen. Tommy R. Franks, the overall commander of coalition forces, said the war was progressing.

Arms Cache Near Basra

A routine stop and search of a pickup truck by British troops led to the biggest weapons find of the Iraqi war.

Amid firewood and scavenged items in the truck, they found an empty ammunitions container. The driver showed them where he found the container -- an abandoned Iraqi army base, about four miles west of Basra, where they discovered hundreds of small arms and grenades, as well as crates of tank shells and mortars. The most significant find: more than a dozen SA-7 heat-seeking surface-to-air missiles.

The British troops found no sign of chemical or biological weapons, although they discovered crates of gas masks and chemical protection suits and containers of packets of atropine, the antidote to the deadly nerve agent VX.

Civilians in Custody

Reacting to the hit-and-run attacks by the Fedayeen and militias on U.S. supply lines, American forces have started rounding up Iraqi men in civilian clothes suspected of being involved with paramilitary squads. Marines patrolling in Nasiriyah and other areas of heavy fighting have detained more than 300 men in civilian clothes.

Military lawyers are drafting new criteria to guide troops on when they should take into custody Iraqis who appear to be civilians. Those detained are being locked up in facilities separate from prisoners of war, until a hearing is held under the Geneva Convention . Any deemed to be POWs will be held until the end of the war and then released.

Those prisoners found to have used civilians as human shields or otherwise violated international laws of war will be deemed "illegal combatants" and shipped to the U.S. naval base at Guantanamo Bay, Cuba, or other facilities.

From Washington

The Pentagon's top military and civilian officials took to the Sunday television talk shows to insist that a major attack on Baghdad remains part of the U.S. war plan, although they said it will not take place until conditions are more favorable to U.S. forces. They rejected arguments from some current and retired military officers that the war had been started with an inadequate number of ground forces.

Defense Secretary Donald H. Rumsfeld and Gen. Richard B. Myers, chairman of the Joint Chiefs of Staff, denied reports that a pause in the rush to the Iraqi capital had been ordered while the southern part of the country is pacified, supply lines are secured and troop reinforcements arrive.

But they stressed that the battle for Baghdad would be tougher than any military engagement thus far. "There are difficult days ahead. Baghdad is not going to be easy," Rumsfeld said.

-- Judy Sarasohn