A new caretaker government, carefully apportioned among Iraq's religious and ethnic groups, assumed temporary authority from the Iraqi Governing Council Tuesday after a month of wrangling.

The U.S.-appointed council then dissolved itself. Before it did, however, it managed to get many of its choices installed in office.

Ghazi Yawar, a U.S. educated tribal sheik and council member, was chosen as the president of the interim government after the U.S. favorite, Adnan Pachachi, turned down the job because he lacked support from council members. The presidency is supposed to be a symbolic or ceremonial office.

The actual political leader of the government will be the interim prime minister, Ayad Allawi. Tuesday Allawi appointed the cabinet that will oversee the transition to what President Bush has called "full sovereignty" on June 30.

"We're grateful to the national alliance led by the Americans who have sacrificed so much to liberate us," Allawi declared at a ceremony where he introduced his cabinet.

President Bush, who took the good news as a cue for a rare and expansive impromptu news conference in the White House Rose Garden, expressed satisfaction with the makeup of the interim government. He noted that the cabinet includes six women and a number of regional Iraqi leaders.

Tuesday's development, the president said, was "a major step toward the emergence of a free Iraq. This is a very hopeful day for the Iraqi people and the American people." Bush said he was particularly grateful that Allawi, at the ceremony, publicly thanked the United States for liberating his country.

Ominously, an explosion and gunfire shook the Convention Center within the protected Coalition Provisional Authority Green Zone just after the announcement of the new president was made by U.N. representative Lakhdar Brahimi, who has been overseeing the selection process. American troops flooded the area and fighter jets streaked overhead. Wire services reported an attack, with three fatalities, on the headquarters of a Kurdish party near the entrance to the Green Zone.

Also on Tuesday, a suicide car bomber killed 11 Iraqis outside a U.S. base near Baiji, about 150 miles north of Baghdad.

"The first request of the people is safety and security," said Brahimi, who could hear and feel the blast near the Green Zone. "But security and stability will not be achieved with weapons alone. The country is in dire need of real political action to bridge the division that was caused by the previous regime," he said at a ceremony officially unveiling the new government.

"Give them a chance. Help them. Judge them after looking at their progress and the actions they take," he said.

A step-by-step conversion to self-government now confronts Iraq.

Under the current plan, the caretaker government will convene an assembly of a thousand people next month. The assembly, in turn, will choose a national council of 100 members that will help oversee the government and exercise veto power over the cabinet council of ministers.

The process is ultimately designed to lead to an election and the formation of a permanent government for Iraq. Analysts universally believe that the caretaker government's success will be determined in part by the extent to which the Iraqi people believe it to be legitimate rather than a U.S. tool. It is also likely to confront an intensification of violence during the transition, U.S. officials believe, that will severely test its stability.

The blast Tuesday underscored the threat, as did preparations for a formal ceremony amid the heavy armored presence of the U.S. Army.

In the 29 days remaining in June, meanwhile, the interim leaders will get on-the-job training to get them ready for June 30.

But there were already signs that they will not be content with that role alone. It was clear Tuesday that Iraq's temporary leaders are determined to influence the wording of the U.N. resolution currently under discussion that will set out the terms of the handover of authority.

Yawar, along with others on the governing council, has been critical of the draft resolution because it gives too little control to Iraqis over security and the activities of U.S. troops.

And Allawi, the prime minister, said his government would "need the partnership of the multi-national force" being considered by the United Nations.

Hoshiyar Zebari, newly appointed as foreign minister on Tuesday, was heading for New York to lobby the United Nations for full sovereignty when the U.S. occupation authority relinquishes power on June 30.

Asked about military control in the post-June 30 Iraq, Bush said, "We'll be flexible." At times, the Iraqis may ask the United States to stay out of a situation, he said. At times, they may ask for help.

In no circumstance, he said, would U.S. troops "in harms way" have to consult with anyone other than their own commanders.

He said the United States has demonstrated in Afghanistan that it can collaborate smoothly on such matters.

During the past few weeks, there were indications of significant disagreement between the U.S. occupying authority and the Governing Council about who would do what in the interim government.

But a senior U.S. official in Iraq, who asked not to be identified, played it down Tuesday. "The interim government that was unveiled today was the result of hundreds of conversations with thousands of people," he said.

While the consultations were "intense," he said there was no pressure applied by U.S. officials.

He said that when L. Paul Bremer, the civilian administrator of the U.S. occupation, consulted the White House about the two top presidential contenders, he was told that "either of them would make an excellent president of Iraq and we don't have a favorite."

Bush said he personally played no role in the choice of the new leaders, saying that Brahimi had made all the decisions.

Iraq is divided ethnically among majority Shiite Muslims, who are concentrated in the south; once-dominant Sunni Muslims, concentrated in the regions north and west of Baghdad; and Kurds, who have their own semi-autonomous region in the far north. Rivalries among the groups are longstanding and intense, as are rivalries within each group.

Yawar, a 45-year-old engineer with a master's degree from George Washington University, is a Sunni Muslim who lived in exile. He is a leader of one of Iraq's largest tribes, the Shamar, whose members include many Shiites as well as Sunnis. Because of that he has had the strong backing of the council's Shiite majority. He also enjoys the support of the council's Kurdish members.

Allawi, is the leader of the Iraqi National Accord, which worked in exile with the CIA for the overthrow of Saddam Hussein. He is a Shiite.

One of two vice-presidents, Ibrahim Jaafari, is the leader of the Shiite Dawa Islamic Party.

The other vice president, Rowsch Shaways, is a Kurd from one of two rival Kurdish political parties.

Barham Saleh, the deputy prime minister for national security, represents the other Kurdish party.

The Bush administration had said it would allow U.N. envoy Brahimi to select the interim government, a task he has been performing in consultation with a wide range of Iraqi organizations and leaders. But council members insisted that Brahimi's role was subordinated by U.S. officials who want a new government that is closely allied with Washington.

Brahimi, in turn, had said he wanted to form an interim government made up largely of politically independent technocrats who would act as caretakers until national elections are held early next year, effectively minimizing the role of politicians from the council. He had not intended to give the council veto power, on the grounds that it lacks broad legitimacy in Iraq.

Tuesday, Brahimi issued the following statement: "Consultations for the formation of the Iraqi Interim Government have been going on without interruption throughout the four weeks which have elapsed since my United Nations colleagues and I returned to Baghdad.

"These consultations have involved the Governing Council, the Coalition Provisional Authority, and a very large number of representatives of the Iraqi public, including political parties, professional associations, trade unions, tribal and religious leaders, academics and intellectuals, women's and youth organizations, and others.

"I am pleased to announce that, on Sunday, I handed over to His Excellency Prime Minister Designate Ayad Allawi my recommendations concerning the composition of his Cabinet."

Fred Barbash reported from Washington.