President Bush demanded yesterday that U.S. military captives in Iraq be treated humanely and said that those responsible for any mistreatment would be treated as war criminals.

Bush's first extended public appearance since last Wednesday, when he announced that military operations in Iraq had begun, came after reports that U.S. ground troops advancing toward Baghdad had encountered stiff resistance. Defense officials also reported more casualties and, for the first time, U.S. troops being taken as prisoners of war.

Arriving from Camp David by helicopter at midday, Bush told reporters on the White House South Lawn he did not yet know all the details of the capture of at least five soldiers from an army maintenance crew, confirmed by the Pentagon after Iraq released a video showing them and the bodies of four others that appeared to be American service members. "I do know that we expect them to be treated humanely, just like we'll treat any prisoners of theirs that we capture, humanely," he said.

Bush's remarks came after White House officials said they had decided to increase his visibility after he had remained out of sight for most of the last several days. They said Bush plans to resume making regular public appearances this week, and will use the events to try to educate and reassure Americans. He is likely to visit a stateside military base to meet with families of military personnel who have been deployed to the Persian Gulf theater, an aide said. The White House officials emphasized that most details of the war will continue to come from the Pentagon and from military briefings in the Persian Gulf region.

In keeping with that decision, Defense Secretary Donald H. Rumsfeld and the Joint Chiefs of Staff chairman, Air Force Gen. Richard B. Myers, dominated the Sunday talk show circuit. But while they strived to communicate the message that the war was proceeding according to plan, both found themselves forced to respond to questions about events that were being reported by journalists on the ground virtually as they were happening.

Shown news footage of Iraqis firing shots into the Tigris River in Baghdad yesterday, and asked on "Fox News Sunday" about reports that a U.S. or British pilot had ejected over the city, Myers said, "No, well, I, I'm trying to interpret what we're seeing there on the videos, but no, there's -- we don't think there's anybody that's been lost." The reports turned out to be false.

On NBC's "Meet the Press," Rumsfeld was asked whether he knew the motives of an American soldier arrested for a grenade attack on a U.S. command tent at dawn yesterday in Kuwait in which an army captain was killed and a number injured. "Oh, of course not," Rumsfeld said. "It just occurred."

On the fourth day of the war, both U.S. and British officials were repeatedly called upon to respond to reports of bad news. In addition to heavy fighting around Nasiriyah, where the most casualties occurred, and the failure to completely secure the southern city of Basra, there were accounts of casualties and captures, as well as the grenade attack. Also, Britain's Ministry of Defense yesterday confirmed reports that a U.S. Patriot missile had mistakenly shot down a Royal Air Force Tornado jet near the Kuwait border Saturday night, killing both crew members. Two previous aerial accidents last week resulted in the deaths of 14 British and five U.S. service members.

Accompanied by national security adviser Condoleezza Rice, White House Chief of Staff Andrew H. Card Jr., and his wife, Laura, Bush returned earlier than scheduled yesterday from Camp David, where he chaired a National Security Council meeting Saturday morning. Although he normally walks without comment past reporters gathered to watch his arrival, he stopped to answer questions that initially focused on the captured and killed soldiers.

"Today, in our church service, Laura and I prayed for . . . those in the coalition forces who lost their lives," Bush said. ". . . It is evident that it's going to take a while to achieve our objective, but we're on course, we're determined, and we're making good progress."

Saying that Iraqi President Saddam Hussein is "losing control of his country," Bush added that it was "important for the American people to realize that this war has just begun. And it may seem like a long time because of all the action on TV, but in terms of the overall strategy, we're just in the beginning phases."

He acknowledged that humanitarian assistance to Iraqis in the southern part of the country has been delayed by ongoing fighting in Basra and around the port of Umm Qasr, but said he had been assured it would begin to arrive within the next 36 hours. "We've got a massive ground assault going on, and right behind it will be a massive movement of humanitarian aid to help the people of Iraq," Bush said.

The immediate distribution of food, water and medical care to portions of Iraq brought under U.S. control is an integral part of the military plan to prevent resentment of the invasion force and quickly convince the Iraqi people they are better off. Reporters reaching the "liberated" town of Safwan near the Kuwait border on Saturday found angry residents in need of humanitarian assistance.

"We understand we have an obligation . . . to put food and medicine in places so the Iraqi people can live a, you know, a normal life and have hope," Bush said. "And that's exactly what's going to happen shortly, when the area's completely safe enough to move the equipment forward."

Giving a general overview, Bush said that oil fields in southern Iraq, which military planners had feared Hussein would try to sabotage, had been secured. "That is positive news for all of us." He said that "most of the south is now in coalition hands. Obviously, there's pockets of resistance in a place like Basra, [but] we're making great progress."

"In the west," he continued, "we're making great progress. The area of the launch sites for the Scuds, while certainly not 100 percent secure, but we've made good progress. And so I can assure the American people, we're making good progress. And I also can assure them that this is just the beginning of a tough fight."

Bush seemed to indicate that his 48-hour ultimatum that Hussein leave Iraq, made Monday, was off the table. "He had his chance," Bush said. ". . . He chose not to go into exile." Asked whether he was surprised that Iraq has not used chemical or biological weapons against invading U.S. and British troops, Bush replied that he was "thankful."

Staff writer Mike Allen contributed to this report.

President Bush: Abuse of captives would be treated as a war crime. The president responded to reports of captures and casualties, saying, "It's going to take a while to achieve our objective, but we're on course . . . and we're making good progress."