AGHDAD, Iraq, Aug. 20 — Sharp differences emerged today between the top American administrator in Iraq and the country's interim government as the United States sought to calm a city unnerved by the truck bomb that killed 20 people in the United Nations headquarters.
Iraqi officials described a tense meeting between L. Paul Bremer III and the Iraqi Governing Council. Mr. Bremer, they said, demanded that the 25-member Council exert more authority, condemn the bombing strongly and communicate better with the Iraqi people.
Mr. Bremer's office did not respond to a request for comment. But a memo prepared by two of his staff and dated today listed measures that the Iraqi Council should be encouraged to take, including calling on Iraqis to "take responsibility for their own security" by joining a newly created Iraqi civil defense force and holding "town hall meetings" in their local districts.
The confrontation clearly reflected a growing American conviction that a greater and more visible Iraqi involvement in government might allay some hostility to the American-led occupation. Iraqi officials said the Council had responded by saying it lacked authority to convince Iraqis it was effective or relevant.
Iraqi Council members have repeatedly said they should be granted more authority over the police force."You can't blame for us anything," said Adnan Pachachi, a council member, in a recent interview. "We don't have any responsibility."
After the meeting, the Iraqi leaders declared a three-day period of mourning for those killed in the attack. Mr. Bremer, in an apparent attempt to force the Council members onto the political stage, was hardly seen today.
The political tensions surfaced as American F.B.I. agents combing the scene today said the truck used in the attack had carried about 1,500 pounds of explosives including mortar shells, hand grenades and a 500-pound Soviet-made bomb. Contrary to earlier reports from witnesses that a cement mixer had been used, the F.B.I. said today that the bomb was carried by a flatbed truck.
Thomas V. Fuentes, the special agent in charge of operations in Iraq, said the munitions had probably been packed on top of the bomb, which was of the kind normally dropped from airplanes.
A flatbed truck was also used in a bombing attack on the Jordanian Embassy earlier this month, he said. The F.B.I. is awaiting chemical analysis to find out if the materiel used in that attack consisted of old Iraqi munitions.
Investigators said they would conduct a chemical analysis of human remains found in the truck debris at the United Nations building to determine how many people were inside.
They added that they would try to trace the vehicle's identification number, but said that the looting of vehicles and the destruction of so many records would make such identification difficult.
The nature of the weapons suggested to some experts here that the authors of the attack included former members of Saddam Hussein's regime, but without proof of such a link or any claim of responsibility, the nature of the organization behind the bombing remained murky.
Ahmed Chalabi, a member of the Iraqi Governing Council, said at a press conference today that he had passed intelligence to the Americans earlier this month indicating that a militant Islamic group had discussed the possible truck bombing of several targets in Baghdad, including the United Nations. American officials here declined to comment.
With their headquarters destroyed, most United Nations workers remained confined to their hotels. United Nations officials said they were not planning a full-scale evacuation but would probably draw down their staff of 350 foreigners by about 10 percent.
Perhaps more would be leaving soon, said Mr. Salim Lone, a spokesman for the organization here.
"Yesterday people were saying let's stay and show them we can't be driven out like that," Mr. Lone said. "There was an element of bravado. I think things are setting in now. There is a lot of tension in the city, with roads blocked off. It's not as if something terrible can't happen again."
Concern was clearly widespread today among Western officials that Iraq could find itself in a political void. The memo prepared for Mr. Bremer suggests that American officials are concerned that in the aftermath of Tuesday's truck bombing, Iraq's leaders might appear disconnected from the tragedy.
"Tell them that the GC needs to be seen governing, not later but now," the memo said, referring to the Governing Council. "Encourage them to come out with a forceful statement," the memo said. "Urge them to undertake an aggressive press outreach strategy," it added.
The apparent tension between Mr. Bremer and at least some of the Council members suggests the delicacy of the political enterprise here. American officials say they are eager to turn over the reins of the Iraqi government to the Iraqi leaders, but not so fast as to overwhelm their untested democratic skills.
But Iraqis seem to feel they are being given power too slowly. "We should have a real government, and then we could begin to solve Iraq's problems," said Adil Abdul Mahdi, senior adviser to Governing Council member Abdul Aziz al-Hakim. "The Americans don't want the help of the Iraqi forces."
With such responsibility, the Iraqis say, they would be able to deflect at least some of the blame away from the Americans for such things as the looting and lack of electricity.
At least one Iraqi Council member challenged what he described as Mr. Bremer's patronizing tone, an official present at the meeting said.
Since the interim government was established on July 13, the 25 members of the Iraqi Governing Council have met several times but taken few concrete political steps.
For several days, they have discussed the appointment of a cabinet to take over the day-to-day running of the Iraqi government, but they have yet to agree on a list of names. They seldom appear in public, preferring instead to gather inside the sheltered confines of what used to be called the Republican Palace.
Some Iraqi officials, including Council members, defended Mr. Bremer, saying that he was merely recommending steps that the Iraqi Governing Council should have taken on its own. They said they were sometimes frustrated by the slow pace of deliberations undertaken by the Council.
"He was telling us that we need to tell the people what we have done," said Dr. Raja Khuzia, a Governing Council member. "We should have done these things anyway."
Officials said today that all of those injured in Tuesday's attack would be taken out of the country immediately, with others to follow.
As in the period right before the American invasion in March, the United Nations faced a problem over how to reduce its staff without appearing to quit the country. Staffers said they were being offered two weeks leave in Amman, Jordan, while the situation stabilized, before a decision was made on whether they should come back.
During special meetings today for expatriate employees, some United Nations staffers said they were determined to stay. Others said they were angered by the poor security under the United States occupation, while still others wept over their missing comrades.
"The situation here is such that the Iraqi people need a lot of help," said Robert Painter, coordinator for humanitarian assistance in Baghdad and two other central provinces. "I don't think we can turn our backs on the humanitarian needs in Iraq."
But others were doubtful, saying that planning United Nations programs seemed futile given the basic lack of security.
"How can you go assess water pollution if you don't know if the program you want can be put in place?" said one woman who was planning to leave. "Security is the most important thing right now. There is very localized security in small pockets and the rest of the country is going to the dogs."