Now on a battlefield of office buildings and bridges instead of desert, U.S. forces faced all the hazards of urban combat today as they expanded their control over Iraq's capital city, Baghdad.

They encountered snipers, looters, holdout remnants of Iraqi military units, militiamen and what appeared to be freelance bandits as they penetrated into the heart of the city. At least two journalists were reported killed when a U.S. tank fired into the Palestine Hotel, headquarters for foreign reporters covering the way.

Reports from journalists in Baghdad and from military commanders told of steady but painstaking progress as elements of the Army's 3rd Infantry Division and the 1st Marine Expeditionary Force moved to join up near the center of Baghdad, an urban agglomeration of 5 million inhabitants.

"We are conducting raids from a couple of directions into Baghdad proper and rooting out resistance wherever we find it," Army Maj. Gen. Stanley McChrystal said at a Pentagon news briefing. The capital is "isolated," and all main routes into the city and out are under U.S. military control, he said. U.S. troops are able to "spend the night where they want to," he said. In addition, the United States has unchallenged supremacy in the air, making it possible to bomb the city wherever and whenever commanders find it useful, he said.

Still, there was abundant anecdotal information from journalists in the city that ground units are confronting a difficult environment. Fighting in close quarters and trying to minimize civilian casualties, the U.S. troops have forfeited a good bit of the overwhelming technological advantage that their advanced weaponry gave them in desert combat.

A Marine convoy moving toward the center of the city from the east got a nasty taste of this new combat, Washington Post correspondent Jonathan Finer reported. As the vehicles approached a vast industrial campus covering dozens of acres of Tigris River frontage, small arms fire whistled overhead. Intelligence reports had indicated Iraqi forces were using the facility as a jumping off point for attacks on U.S. Army troops on the other, western side of the Tigris.

When the convoy arrived at a large warehouse compound and Marines dismounted to clear it, the air was almost immediately filled with gunfire: the pop of M-16 rifles and intermittent cracks of responding AK-47 assault rifles were nearly drowned out by the staccato of .50-caliber machine guns.

Marines used shotgun blasts to open locked doors as they passed from building to building. An unarmed, elderly security guard who ducked into a hut and attempted to make a phone call was apprehended for questioning by interrogation specialists. Tanks rumbled up and down the streets, providing support for troops on the ground.

Marine snipers played a major role in the operation, moving catlike along the rooftops, searching out enemy targets. They reported having killed nine for sure and possibly up to 14 Iraqi defenders.

"We know that as we conduct operations inside of Baghdad, we should anticipate attacks from unexpected locations, that some of the military actions might be unconventional in nature, whether it's the use of car bombs, or whether it's ambushes, the use of snipers, or certainly the consistent pattern we've seen elsewhere of using civilian shields," Army Brig. Gen. Vincent K. Brooks said at the daily press briefing at U.S. Central Command field headquarters in Doha, Qatar.

Brooks described firing on the journalists' hotel as almost inevitable in an environment where the beleaguered remnants of Iraqi President Saddam Hussein's forces are firing on U.S. troops from hotels, schools and religious sites.

"We know that we're conducting operations inside of an urban area, an area where the regime has chosen to deliberately defend and not stand down," Brooks said. "And we can only be reminded that the risk increases for the population as we do these operations."

News agencies identified the journalists killed in the shelling of the hotel as Taras Protsyuk, 35, a cameraman for the Reuters news agency, and Jose Couso, 37, a cameraman for a Spanish television network.

A third journalist, al-Jazeera cameraman Tarek Ayoub was killed earlier in the day when a bomb dropped during a U.S. air raid hit the Arab satellite television station's office in the Iraqi capital. Another al-Jazeera staffer was wounded.

Some Arab journalists speculated that the strike was intentional and meant to send a message to the al-Jazeera, which has reported extensively on the human suffering caused by the war, and has angered U.S. officials for airing video of American POWs.

"As to whether it was a deliberate attack or not, we can't ascertain at this time," said Sheik Hamad Bin Thamer Al Thani, chairman of al-Jazeera. "We will see if there is any investigation or any conclusion forwarded to us about what happened."

Brooks said that the decision to open fire on the Palestine Hotel was taken on the ground by a tactical commander and was not ordered by senior commanders. U.S. military officials at Centcom said the journalists bore some responsibility for their own deaths because they continued working in Baghdad even after U.S. officials warned them in the days leading up to the war they should pull out for their own safety.

"We don't know every place a journalist is operating on the battlefield. We know only those journalists that are operating with us. And we have always said that the area for combat operations is a very dangerous place indeed. And certainly there should be no surprise in anyone's mind that eventually operations were going to close on Baghdad," Brooks said.

According to a statement issued by Centcom, "Commanders on the ground reported that Coalition forces received significant enemy fire from the Palestine Hotel in Baghdad and, consistent with their inherent right of self defense, Coalition forces returned fire. Sadly, a Reuters and a Tele 5 (Spain) journalist were killed in this exchange."

Centcom offered a similar explanation for the strike against the office of al-Jazeera:

"According to commanders on the ground, Coalition forces came under significant enemy fire from the building where the al-Jazeera journalists were working and, consistent with the inherent right of self-defense, Coalition forces returned fire. Sadly, an Al Jazeera correspondent was killed in this exchange."

Hamad -- a member of the ruling family of Qatar, which is hosting the headquarters of U.S. Central Command -- rejected the explanation provided by U.S. military officials that both the al-Jazeera bureau and the Palestine Hotel were struck because U.S. troops came under fire from those buildings.

"This is absolutely and categorically denied by our reporters and other reporters on the ground, both at our bureau and at the Palestine Hotel," he said.

Some journalists who have been operating from the Palestine Hotel, including Anthony Shadid of The Washington Post, were not in the building at the time.

Shadid reported today that there were "conflicting reports" about what happened at the hotel. Some journalists who were at the hotel said there was no sniper fire from the hotel before U.S. troops fired on it.

Similarly, National Public Radio's Anne Garrells reported today that she had "seen no snipers in my hotel, and I've heard no outgoing shooting from this hotel." However, she said, she had seen journalists on the rooftop with binoculars observing the war.

Many of those journalists today traveled to view the immense crater left by U.S. bombs that targeted a compound in a residential neighborhood where Hussein and his two sons were believed to be meeting other officials of the ruling Baath Party on Monday.

A member of the crew of the B-1 bomber that carried out the strike said in a telephone interview with Washington Post reporter Bradley Graham that an air controller who directed the attack told them, "This could be the big one." But it is not clear whether Hussein or any regime officials were present when the airstrike occurred.

"We had credible information that there was a regime leadership meeting occurring yesterday," Brooks said. "As to who was inside and what their conditions are, it will take some time before we can make that full determination." The bombing apparently indicates that U.S. military officials have finally decided that Hussein survived a missile strike on another Baghdad compound on the first night of the war, two and a half weeks ago.

Shadid said there were civilian residences in the bombed compound and that as many as 13 civilians were killed.

Bulldozers rumbled over man-made hills of rubble today in the wealthy neighborhood of Mansour. They lurched, careful not to fall into a crater 30 feet deep and as long across.

The Iraqi government's reaction was much different than after the first attempt on Hussein's life on the first day of the war. Today, unlike then, the Iraqi Information Ministry escorted journalists to the site. Reporters who arrived today unexpected were given free rein to inspect it and interview residents -- many of them sobbing relatives and friends of people believed to have been buried in the strike.

Elsewhere in the capital, Shadid reported, most electricity and water service is out, and Iraqi television has been knocked off the air. He reported that the capital's residents now appear to understand that U.S. troops are in their midst and will soon take over the entire city.

In Geneva, the World Health Organization said Baghdad's hospitals have been overwhelmed by the influx of casualties and are unable to treat the mounting cases of burns and trauma. WHO has a convoy of supplies waiting in Jordan but has been unable to send it to Baghdad because of the security situation, an agency spokesman said.

President Bush said he did not know if the Iraqi leader survived the airstrike. "The only thing I know is, he's losing power," Bush said at a joint news conference with British Prime Minister Tony Blair in Belfast, Northern Ireland. "That grip I used to describe that Saddam had around the throats of the Iraqi people [is] loosening. I can't tell you if all 10 fingers are off the throat, but finger by finger it's coming off. And the people are beginning to realize that. It's important for the Iraqi people to continue to hear this message: We will not stop until they are free."

Bush spoke emphatically about the emotions of the Shiite Muslim people of southern Iraq, who rose against the Hussein regime at U.S. urging after the 1991 Persian Gulf War -- when Bush's father was president -- only to be crushed when expected U.S. military aid did not intervene.

"Now, these are people in the south of Iraq that had been betrayed, tortured, you know, had been told they were going to be free, took a risk in the past and then were absolutely hammered by the Iraqi regime," he said. "They were skeptical. They were cynical. They were doubtful. And now they believe. They're beginning to understand we're real and true."

Bush spoke after two days of meetings with Blair, his strongest ally in the Iraq campaign, in which they agreed that the United Nations will have a "vital role" in managing postwar Iraq. The question of who will manage the reconstruction of Iraq and how a new government will operate has become a new source of disagreement between Washington and the European nations that opposed the war, with Blair in the middle. In his comments today, Bush accepted a United Nations role, which Russia, France and Germany have been demanding, but he was vague on details.

Bush rebutted articles in the U.S. press saying that his administration plans to exert full and unilateral control over Iraq in the immediate aftermath of the war.

"Forget it," he said. "From day one we have said the Iraqi people are capable of running their own country. That's what we believe. The position of the United States of America is the Iraqis are plenty capable of running Iraq. And that's precisely what's going to happen."

Asked what he meant by "vital role" for the United Nations, Bush said, "We mean a vital role for the United Nations in all aspects of the issue, whether it be humanitarian aid or whether it be helping to stand up an interim authority." He said this "interim authority" will be a "transition quasi-government until a real government shows up, until conditions are right for the people to elect their own leadership."

The fact that Bush and Blair focused their discussions on postwar planning was an indication of their confidence that the war itself is drawing to an end. Although some Iraqi units are still putting up determined resistance, and allied troops are vulnerable to snipers and hit-and-run guerrilla-style attacks, the Iraqi government's ability to sustain itself appears to be evaporating.

Paradoxically, the threat to allied troops appears to be increasing. In the drive across the desert, they had clear views of Iraqi defenders who could be targeted for devastating airstrikes. In the cities, they are vulnerable to small attacks from unseen foes who can disappear into buildings and alleyways. A single fighter with a rocket-propelled grenade launcher can halt a U.S. convoy and inflict casualties by taking out a Bradley Fighting Vehicle or a Humvee.

Perhaps the most intense fighting reported on Tuesday was near the town of Hilla, near the ancient city of Babylon, about 60 miles south of Baghdad. News agencies reported that U.S. troops there called in bombing strikes and helicopter gunships in an effort to crush resistance by remnants of the Iraqi Republican Guard.

Fighting was also reported in northern Iraq, where Kurdish irregulars are advancing from Kurdish-held territory toward retreating Iraqi units near the key city of Mosul. U.S. warplanes bombed Iraqi defensive positions in Kirkuk, an important oil center.

An Iraqi soldier who surrendered after the U.S. air onslaught, said morale in the Iraqi army was at rock bottom.

"They are devastated, they are ruined psychologically," Haidar Hatan Khthair told the Reuters news agency in the village of Pir Daud where he was being held by Kurdish guerrillas known as peshmerga.

Looking hungry and exhausted, he agreed to talk to Reuters as the fighters gave him bread and water.

"I saw many officers ripping off their epaulettes and throwing down their arms," he said. "They have no spirit to fight."

According to Brooks, the Centcom briefer, Special Operations forces from the U.S.-led coalition are preventing Iraqi troops in the north of the country from reinforcing other Iraqi units in Tikrit, Saddam Hussein's home town, and Baghdad. In a battle near the demarcation line between Kurdish- and Iraqi-held territory on Monday, special forces with close-air support destroyed an Iraqi force equipped with tanks and armored personnel carriers. In a similar engagement near Kirkuk, special forces turned back and Iraqi counterattack, destroying tanks, trucks and armored personnel carriers.

Most of the battles have pitted U.S.-led forces against relatively small Iraqi formations of between 20 to 60 vehicles, Brook said. Many of these vehicles are so-called technicals, trucks with mounted machine guns.

Aside from the condition of Saddam Hussein, the major uncertainty of the moment is whether the buried metal drums U.S. troops found yesterday near Karbala constituted a store of chemical weapons. Brooks said Centcom is waiting for samples of the material to be tested.

"We don't know enough at this point to say that it should be discounted or that indeed we found some weapons of mass destruction available for use. So at this point we're simply remaining in waiting until we have additional information," he said.

In Basra, Iraq's second largest city, in the far southeastern corner of the country, British troops began large-scale distribution of drinking water to a thirsty and restive populace. Wherever the 10 huge tanker trucks stopped to dispense their precious cargo in the searing heat, they were mobbed by people carrying whatever containers they could get, Reuters report.

Now fully in military control of the city, British troops have not been able to stop the wave of looting that erupted when the last vestiges of central government authority evaporated over the weekend.

Col. Chris Vernon, chief spokesman in Kuwait for the British forces, said they had identified a local sheikh, or respected elder, to take on the task of municipal administration. He declined to identify the sheikh.