Laying the groundwork for an advance on Republican Guard divisions ringing Baghdad, U.S. troops clashed with Iraqi soldiers and militiamen at flash points along a 150-mile slice of central and southern Iraq today in an effort to protect supply lines, soften defenses and eliminate rear-guard resistance before heading for the capital.

U.S. warplanes and cruise missiles again bombarded Baghdad, striking a presidential palace, an intelligence complex and a training center for paramilitary forces. As the air attacks rattled the capital another day, the ground troops mounted operations in and around four key cities to the south -- Nasiriyah, Samawah, Najaf and Karbala -- to suppress Iraqi army and paramilitary units threatening U.S. troops moving north. The American attacks led to gun battles, artillery exchanges, and helicopter assaults and airstrikes by U.S. and British jets flying close-air support.

At the U.S. Central Command's field headquarters in Doha, Qatar, Gen. Tommy R. Franks, the overall commander of U.S. and British forces, declared that the war is progressing on schedule, vigorously responding to criticism that the military campaign seems stalled after an initial swift advance. "We are in fact on plan," Franks said at a news conference. "Where we stand today is not only acceptable in my view, it is truly remarkable."

In particular, Franks disputed suggestions that the advance on Baghdad has moved into an "operational pause," saying: "It's simply not the case. There is a continuity of operations in this plan. That continuity has been seen. It will be seen in the days ahead, and it will be manifested on the battlefield in Iraq at points and times of our choosing."

Many front-line troops, who have sped to within 50 miles of the Iraqi capital, have spent the past few days resting and getting resupplied. Some of their generals have suggested that tough resistance means more troops should be thrown into the fight before an all-out assault on Baghdad. But today's activities indicated the U.S. forces have been far from static even as debate rages about what to do next.

Lead units of the 3rd Infantry Division, at the tip of the U.S. spear aimed at Baghdad, pushed to Hilla, just southeast of Karbala, after overnight airstrikes scattered three Iraqi army mechanized and tank units guarding the city. Militiamen armed with assault rifles and rocket-propelled grenade launchers tried to stop the advance, but they were beaten back by a barrage of artillery and rockets, allowing additional elements of the 3rd Infantry to move within striking distance of the Republican Guard's Medina Division arrayed north of Karbala.

[Early Monday, the Associated Press reported that elements of the 4th Battalion of the 64th Armored Regiment entered the town of Hindiyah, 50 miles south of Baghdad, where they captured several dozen Iraqis who identified themselves as members of the Republican Guard. At least 15 Iraqi troops were killed in the fighting.]

In Najaf, along the Euphrates River about 100 miles south of Baghdad, troops from the 1st Brigade of the 101st Airborne Division used artillery and called in airstrikes to target militiamen who have been responsible for repeated attacks on U.S. military supply lines. The 101st also secured an airfield near the city, although some of the division's AH-64 Apache attack helicopters were forced to abandon their missions after coming under Iraqi fire.

In Samawah, also along the Euphrates but 50 miles farther south, two battalions from the 82nd Airborne Division engaged in often intense fighting as they pursued an estimated 1,000 paramilitary fighters holed up in the city. And a Marine raid secured buildings held by Iraq's 11th Infantry Division in Nasiriyah, a riverfront city another 50 miles to the south that has been the scene of fierce fighting over the last week.

The Central Command reported that in one building, Marines found more than 300 chemical suits and masks, injectors for the nerve agent antidote atropine, two decontamination vehicles and other decontamination devices. In another, they discovered more than 800 rocket-propelled grenades, along with mines, mortar and artillery rounds and rifle bullets. Earlier, Marines found chemical suits and masks, weapons and ammunition inside a hospital in Nasiriyah that U.S. officials said was being used as a staging area for paramilitary forces.

In the southern port city of Basra, British troops reported finding a cache of training equipment for chemical warfare, including a Geiger counter, nerve gas simulators, gas masks and protective suits.

Although the discoveries suggested that Iraqi forces were prepared for chemical warfare, it was unclear when the equipment was deployed; U.S. forces have found no chemical or biological weapons since the invasion of Iraq began with airstrikes March 20.

British troops on the southern and western edges of Basra exchanged artillery fire with Iraqi forces, but they have refrained from a full-scale invasion of the city because of fears it could lead to bloody urban combat. At the same time, the troops began what one British defense official called "aggressive patrolling" inside the city.

Group Capt. Al Lockwood, a spokesman for British forces in the Persian Gulf region, said Royal Marine commando units staged raids to target militiamen and soldiers who continue to control the city. The operation was called "James," after the fictional spy James Bond.

The first to be nabbed, British defense officials said, were five Iraqi military officers. The commandos also killed a Republican Guard colonel who British officials believe was sent to Basra to "try and strengthen the resolve among the Baath Party militia and the paramilitaries that are operating in the area," Lockwood said.

An Iraqi official in Baghdad denied both claims.

British and U.S. officials said their troops have received increasing assistance from Iraqi civilians in identifying Baath leaders and other loyalists of the president, Saddam Hussein. "As we win the trust of the Iraqi people," said British Maj. Gen. Albert Whitley, "they're pointing these people out, and either we're targeting them or we're detaining them."

In Kuwait, meanwhile, an Egyptian electrician drove a pickup truck into a group of U.S. soldiers standing outside a store at Camp Udairi, an American military base in the Kuwaiti desert, wounding 15. U.S. officials would not say whether the incident, which is under investigation, was accidental or deliberate. But a Kuwaiti law enforcement official said the man, who was working at the camp, appeared to have targeted soldiers in response to the invasion of Iraq.

Fourteen of the injured were treated at the scene for minor injuries; officials expected one soldier to be flown to Germany for treatment of a knee injury.

U.S. and British soldiers manning vehicle checkpoints in Iraq, or otherwise interacting with civilians, were in a heightened state of alert today after a suicide attack Saturday that killed four U.S. soldiers. "We'll have to shut roads down," said Maj. Gen. Buford C. Blount III, the 3rd Infantry's commander. "That's unfortunate, but it's going to be necessary to ensure the safety of our soldiers."

The Pentagon has identified 43 U.S. military personnel killed or missing in action, with more than 100 wounded. But the military's counts, as they churn through bureaucracy and await notification of families, have often lagged behind battlefield reports. Three more Marines were killed accidentally today, bringing the total to more than a dozen, when a UH-1 Huey helicopter taking off after refueling crashed, officers said.

Lt. Gen. Hazem Rawi, a senior Iraqi defense official, said in Baghdad that Saturday's bombing marked "the beginning of a long path of jihad for Iraqis and Arabs against the invaders." He said more than 4,000 volunteers have come from other Arab countries to participate in suicide attacks.

The airstrikes on Baghdad targeted military facilities at the Abu Garayb presidential palace, the Karrada military intelligence complex and the barracks of a paramilitary training center, according to Central Command. Several telephone exchanges in the city and a train carrying Republican Guard tanks also were struck, U.S. officials said.

[Early Monday, a cruise missile hit the roof of the Information Ministry, smashing glass panels and damaging satellite dishes. It was the second attack in three days to target the ministry.]

Although punishing airstrikes in recent days have destroyed much of Baghdad's air defenses, they have done less to damage Republican Guard units defending the capital, according to a U.S. military assessment.

Nightly bombing in the capital has smashed missile batteries, antiaircraft guns, radar and other installations used to target aircraft, giving U.S. pilots far greater latitude in where, when and how high they can fly without risk. Iraqi forces have stopped turning on what remains of their radar for fear of it being destroyed, U.S. officers said, leaving them to shoot almost blind.

So far, however, the air campaign has yet to inflict the level of damage on Republican Guard defenses that ground commanders want to see. Analysts say they believe Iraq has been able to reinforce the divisions around Baghdad to compensate for losses caused by U.S. warplanes, sending in armor or artillery to take the place of equipment blown up by precision-guided bombs.

Three Republican Guard divisions defend the approaches to Baghdad: the Medina Division to the south, the Al Nida Division to the east and the Baghdad Division farther east around the city of Kut. The U.S. Army's 3rd Infantry Division has massed on the southern reaches of Baghdad, while the 1st Marine Division is approaching from the southeast.

Speaking to reporters for the third time since the war began, Franks sought to reassure skeptics about the progress of the campaign, which has encountered stiffer Iraqi resistance than some U.S. commanders had anticipated. He opened by listing several objectives that have been achieved: the swift advance of U.S. ground forces, the capture of Iraq's southern oil fields, the ability of aircraft to fly missions over the entire country with little resistance from antiaircraft defenses, the basing of some air operations within Iraq and the destruction of what he called a "massive terrorist facility" in northern Iraq used by a radical Islamic group called Ansar al-Islam.

"The regime is in trouble and they know it," Franks said.

Franks played down a number of published reports that have suggested disagreement between military commanders and civilian officials about war planning. Franks denied one report that he had asked the Pentagon to delay the attack after Turkey's government rejected a U.S. request to base troops there. He also disputed a New Yorker magazine article to be published Monday saying he was overruled by Defense Secretary Donald H. Rumsfeld about the size of the invasion force and schedule of the attack.

"There are very few people who know the truth of how this plan was put together. In fact, no one has driven the timing of this operation except the operational commander," Franks said, referring to himself.

He said he decided to launch the war on Iraq with a ground offensive in southeastern Iraq because he saw an opportunity to capture the Rumaila oil fields before they were destroyed by Hussein's government. Franks said he had several options for starting the military campaign but the threat to the oil fields determined when and how the U.S.-led invasion began.

"We sensed that we had an opportunity to get these oil fields," Franks said. "Since we had a plan that enabled us to either do air operations first or ground operations first, or perhaps special operations first, we simply put the mosaic together in a way which you have seen unfold."

Sipress reported from Qatar. Correspondents Rick Atkinson, Peter Baker, William Branigin and Monte Reel with U.S. forces in Iraq contributed to this report.

Militiamen captured during fighting along Highway 9 sit under guard by U.S. military police at dusk while waiting for transport to a southern holding camp.Soldiers from the British 40th Commandos fire an antitank rocket as forces with the Queen's Dragoon Guards come under fire from rocket-propelled grenades near Basra, which has been the scene of intense fighting. A British soldier leads an Iraqi man away for questioning outside the southern city of Basra. British troops began a program of "aggressive patrolling" inside the city and exchanged artillery fire with Iraqi forces on the southern and western outskirts. Head of U.S. Central Command, Gen. Tommy R. Franks, points to areas on a map of Iraq as he briefs reporters on the war's progress at Central Command field headquarters in Doha, Qatar.