A diverse group of secular figures, political independents and technical specialists was appointed Tuesday to serve as Iraq's caretaker administration after the U.S. occupation relinquishes authority at the end of this month.

But the U.N. envoy entrusted by the White House to form Iraq's interim government failed to seat his choice for president because of stiff opposition from Iraqi leaders, forcing him to select Ghazi Yawar, a 45-year-old Sunni Muslim tribal sheik who has no government experience beyond a 10-month stint on the U.S.-appointed Governing Council.

The envoy, Lakhdar Brahimi, had offered the largely ceremonial presidency to Adnan Pachachi, 81, a former foreign minister and also a Sunni. But Pachachi turned down the job on Tuesday morning after determining that the government should not begin under a cloud of dissension.

The newly appointed interim administration assumed responsibilities from the Governing Council, which dissolved itself on Tuesday morning so the new government could start work immediately. Iraq's interim leadership will face the daunting challenges of stabilizing this violence-wracked nation, winning over a skeptical population, working out a security agreement with the United States and preparing for general elections early next year.

Reminders of those hurdles were evident on Tuesday, as numerous Iraqis voiced doubts about Brahimi's selections and a car bomb exploded near the headquarters of the Patriotic Union of Kurdistan, killing at least five people and injuring 20. A roadside bomb detonated near a U.S. base in the northern city of Baiji, killing 11 Iraqis, including seven members of the Civil Defense Corps, and wounding more than 22 people, including two U.S. soldiers.

Mindful of the difficulties confronting the new government, Brahimi beseeched Iraqis to support their interim leaders. "Give them a chance," he said at a ceremony announcing his appointments. "Help them. Judge them after looking at their progress and the actions they take. The country needs real national unity."

Brahimi also formally appointed Ayad Allawi as prime minister. He was nominated by the Governing Council on Friday. Allawi, a Shiite politician whose party had been supported in exile by the CIA, also was not Brahimi's first choice, but U.N. officials said Brahimi was compelled to support him after intense pressure from the council.

In addition to the prime minister and the president, the new government includes two vice presidents and a 32-member cabinet. A 100-member assembly that will have veto power over the cabinet's decisions is to be chosen by delegates to a national conference in July.

At the announcement ceremony before 400 Iraqi and foreign guests, including the U.S. civilian administrator of Iraq, L. Paul Bremer, Yawar pledged to rise "above sectarianism and divisions" to build a "pluralistic, federal and democratic Iraq" free of "totalitarianism and discrimination."

Dressed in a flowing white Arab robe with gold fringe and a traditional tribal headdress, Yawar said he would focus the government's energies on restoring security and preparing for national elections early next year.

Allawi, the prime minister, said there was still a need for international military forces "to help in defeating the enemies of Iraq," taking a position favored by the United States but opposed by many Iraqis. He said his government would enter into security agreements with "our allies."

At the White House, President Bush praised the new government, saying its selection "brings us one step closer to realizing the dream of millions of Iraqis: a fully sovereign nation with a representative government that protects their rights and serves their needs."

Bush and other senior U.S. officials expressed satisfaction with Allawi's comments about security cooperation with the United States. The officials also said they were optimistic that Yawar, who served on the Governing Council's security committee, would support the continued presence of U.S. forces in Iraq despite saying in a recent television interview that he blamed "the United States 100 percent for the security in Iraq."

"I can tell you firmly and without any contradiction, this is a terrific list, a really good government, and we are very pleased with the names that have emerged," said Bush's national security adviser, Condoleezza Rice. "These are not America's puppets. These are independent-minded Iraqis who are determined to take their country to security and democracy."

U.N. Secretary General Kofi Annan called the interim government "a new beginning." But he also hinted at the pressure Brahimi faced.

"I think we all have to recognize that the process wasn't perfect and it was a difficult environment," Annan said. "And I think given the circumstances, I believe Mr. Brahimi did as best as he could."

Although Brahimi's decisions were made in secret, in consultation with senior U.S. officials and a handful of Iraqi leaders, he insisted the final product was the result of broad input from Iraqis. He said he met "hundreds, if not thousands of people and consulted with them" about the formation of the interim government.

Despite the council's influence in the selection of Allawi and Yawar, Brahimi appeared to have a freer hand in selecting cabinet members. Six of the new ministers are women and several are technocrats, reflecting Brahimi's desire for an administration without political affiliations. Only six of the 32 belong to large political parties.

Although Brahimi consulted with Allawi on cabinet appointments, a senior U.N. official said all but two of the ministers were chosen by Brahimi. Most of the ministers appointed by the Governing Council last year were removed, including three who were close to fundamentalist Muslims and two with connections to Ahmed Chalabi, the Iraqi politician who used to be a favorite of the Pentagon but has become an opponent of the U.S. occupation.

Chalabi, once regarded by some in the U.S. government as Iraq's president in waiting, did not attend the ceremony. No one from his Iraqi National Congress party was appointed by Brahimi.

The two vice presidents, Ibrahim Jafari of the Dawa party and Rowsch Shaways of the Kurdistan Democratic Party, are politicians, but they represent key constituencies -- conservative Shiites and ethnic Kurds.

Another senior Kurdish politician, Barham Salih, who served as Washington representative of the Kurds' autonomous region in northern Iraq during the 1990s, was appointed deputy prime minister. Leaders of Iraqi's Kurdish minority had sought either the presidency or the prime ministership but agreed to accept one of the vice presidential posts and two senior ministries. Another Kurd, Hoshyar Zubari, will continue to serve as the foreign minister.

Although it took over from the Governing Council on Tuesday, the new administration will be subordinate to the U.S. occupation authority until June 30, when the United States hands over limited authority. The next 29 days are regarded by U.S. officials as on-the-job training for the new government.

But there were already signs that participants would not be content with that role alone. Members of the new administration said they would attempt to influence the wording of a U.N. Security Council resolution that will set out the terms of the handover. Shaways said Zubari, who was traveling to U.N. headquarters in New York, would urge the Security Council to give the new administration full control of Iraqi security forces, a step the Bush administration has been resisting because it deems the country's army and police force unready for full autonomy. Yawar and other Iraqi leaders also want the new government to have greater control over the activities of U.S. troops in Iraq.

Asked about military control after June 30, Bush said: "We'll be flexible." At times, he said, the Iraqis may ask the United States to stay out of a situation; at other times, they may ask for help. But in no circumstance, he said, would U.S. troops "in harm's way" have to consult with anyone other than their own commanders.

During the past few weeks, there were indications of significant disagreement between the Governing Council and the trio of officials sorting out the transition: Brahimi, Bremer and White House envoy Robert D. Blackwill. Council members sought to play a central role in the process, while Brahimi and the U.S. officials wanted to broaden consultations to include provincial, tribal and religious leaders not represented on the council.

Tensions peaked when council members received word of Brahimi's initial choices for prime minister and president. The U.N. envoy had wanted to appoint Hussain Shahristani, a Shiite nuclear scientist, to the prime ministership, but Shiite politicians balked last week, forcing Brahimi to choose Allawi, whose candidacy had the support of U.S. officials.

When Brahimi sought to give the presidency to Pachachi, the council once again objected and insisted that the job go to Yawar. Both were on the Governing Council, but many members argued that Yawar, a civil engineer who lived in Saudi Arabia until the fall of Saddam Hussein's government, was a better choice. He is a leader of a large tribe, the Shamar, which includes both Sunnis and Shiites. He also was regarded by council members as more independent and less supportive of U.S. policies in Iraq than Pachachi.

A brief biography of Yawar distributed by the occupation authority stated that he studied at Georgetown University, but Laura Cavender, a university spokeswoman, could not confirm that he ever attended the school.

Brahimi, a former foreign minister of Algeria, was convinced that Pachachi, a diplomat who had been active in the exiled opposition to Hussein, would make a better president. Despite Yawar's support in the council, the U.N. envoy regarded Pachachi as more popular among other groups of Iraqis. "He was the top choice," an official involved in the process said. "He had much more support among the public at large."

After lengthy negotiations with Yawar, Allawi, other Iraqis and U.S. officials, Brahimi decided to offer the presidency to Pachachi. But when he formally conveyed the offer on Tuesday morning, Pachachi demurred.

"The president should be a force for unity, not division," Pachachi said.

Less than a half-hour later, Brahimi offered the job to Yawar, who immediately accepted. Asked about the contest between himself and Pachachi, Yawar said: "It was in a very friendly team spirit."

U.N. and U.S. officials said Brahimi did not offer the job to Pachachi with the expectation he would turn it down, although there were indications over the weekend that Pachachi was having second thoughts. "There was a hope he would accept," the official involved in the process said. "We didn't know for sure what he would say until the very end."

A senior Bush administration official in Baghdad said the U.S. government did not push for one candidate over the other. "We didn't lobby anybody," the official said. "We thought either one of them would make a fine president of Iraq."

Staff writer Robin Wright in Washington contributed to this report.

Ghazi Yawar, in tribal headdress, is congratulated by supporters in Baghdad after the announcement that he would be Iraq's interim president. Iraqis of the Shamar tribe celebrate the selection of Ghazi Yawar, a tribal sheik, to become interim president of Iraq. The tribe includes both Sunnis and Shiites. Lakhdar Brahimi, the U.N. envoy for Iraq, had offered the position of interim president to Adnan Pachachi, a U.S.-backed official who declined the post in the face of opposition from other Iraqi Governing Council members.