ASHINGTON, March 25 — Some of the Army mechanics captured on Sunday after they took a wrong turn in the Iraqi town of Nasiriya were apparently executed by their captors, probably in front of townspeople, American officials charged tonight.The officials cautioned that the information was based on one source, apparently a communications intercept, and that they were seeking corroborating evidence. It is unclear how many of the seven soldiers were executed, rather than killed in fighting, as the Iraqis contend. Five other Americans were taken prisoner and at least three were still missing.
The accusations came a few days after a videotape of the prisoners and the dead soldiers was broadcast on Al Jazeera, the Arab satellite television network. It showed images of at least four bodies; some appeared to have bullet wounds to the head.
"When the full story comes out, people will be outraged," said one senior military official.
The accusations came at the end of a day in which senior White House and Pentagon officials accused the Iraqis of a number of war crimes, including feigning surrender and then shooting at American forces, and using a hospital as a staging area for military operations.
The White House also said that Iraqi paramilitary forces were preventing relief supplies from reaching Basra in southern Iraq.
At the Pentagon today, Defense Secretary Donald H. Rumsfeld and the chairman of the Joint Chiefs of Staff, Gen. Richard B. Myers, repeatedly defended their war plan against criticism that it had stretched ground forces too thin, leaving their rear areas vulnerable to guerrilla attacks by paramilitary forces.
"It's a good plan, and it is a plan that in four and a half or five days has moved ground forces to within a short distance of Baghdad," said Mr. Rumsfeld, after repeated exchanges with reporters. "And forces increase in the country every minute and every hour of every day," he said.
General Myers called the war plan "brilliant," saying any setbacks were due to Iraqi violations of the Geneva Convention. "It's a plan that's on track," he said. "It's a plan everybody had input to. It's a plan everybody agrees to."
A senior administration official who was deeply involved in war planning said in an interview today that President Saddam Hussein's loyalists "fight like terrorists," and attributed the absence of a welcome for American troops to "a reign of terror in some of these cities, with these paramilitary and special security organizations enforcing the same brutal terror they have been enforcing for years."
"We haven't encountered large segments of the Iraqi population yet," the official cautioned.
The official said that Mr. Bush had decided to assume the Iraqi government "is still functioning." But the official compared the first six days of this war to the invasion of Afghanistan in 2001, saying, "the surprise is the speed of our advance."
Despite the optimism at the Pentagon and the White House, today was the first day the administration found itself somewhat on the defensive about its strategy.
The cause appeared to be the combination of unexpectedly fierce resistance around Basra, the lost convoy, and the effectiveness of the Republican Guard in warding off Apache attack helicopters with a curtain of small-arms fire.
Mr. Bush tried to show optimism this morning, when he traveled to the Pentagon for a briefing, but he cautioned: "We're fighting an enemy that knows no rules of law, that will wear civilian uniforms, that is willing to kill in order to continue the reign of fear of Saddam Hussein."
Later, his spokesman, Ari Fleischer, said that the delay in getting aid to southern Iraq was the fault of the Iraqi authorities. "We didn't expect the Iraqis to cease caring about their own people, to cease feeding their own people, to put up impediments to this humanitarian relief supplies," he said.
The White House also used Mr. Bush's visit to press Congress to pass a $74.7 billion appropriation to finance the war and reconstruction. The Office of Management and Budget made it clear that it was profitable for nations to be members of Mr. Bush's "coalition of the willing," even if some were only reluctantly willing.
Turkey, which denied American access to its bases to open a northern front against Iraq, would receive $1 billion in economic aid under Mr. Bush's plan, allowing it to get up to $8.5 billion loans or loan guarantees.
Israel would also get $1 billion in direct military assistance and $9 billion in loan guarantees. Jordan would receive $700 million in economic aid, and Egypt $300 million in grants, allowing it to obtain up to $2 billion in loan guarantees.
President Bush's greatest ally in the war, Prime Minister Tony Blair, prepared to come to Washington on Wednesday for a summit meeting that the British leader said would focus not only on war strategy, but on "how we get America and Europe working again together as partners and not as rivals."
The disputes that marked the battle over a second resolution at the United Nations authorizing war — an effort the United States, Britain and Spain abandoned — have now given way to a new dispute over how to administer Iraq after the war.
The president's national security adviser, Condoleezza Rice, flew to New York yesterday to discuss that subject and Iraq's relief needs with Secretary General Kofi Annan.
The visit came as sharp disputes were arising among the members of an expert committee designated to shape a Security Council resolution reconstituting the oil-for-food program that was suspended on March 17 when the United Nations personnel were withdrawn from Iraq.
The dispute has delayed the authorization of new mechanisms for the distribution of relief aid, including about $2.4 billion worth of food and other supplies being sent to Iraq.
The diplomatic struggle, pitting Russia and Syria against the United States and Britain, focuses on control over contracting authority in the program and on whether the resolution would legitimize the military action after the fact.