Iraq's fragile new government faces its first big political test this week: holding a national conference that is a pivotal element of the country's postwar evolution but that U.S. and Iraqi officials fear may be boycotted by key players, hijacked by religious parties, targeted by insurgents or simply overwhelmed by bickering.

The three-day conference of 1,000 Iraqis is scheduled to begin Thursday, Iraqi officials said. Its goal is to select a council of 100 members that would oversee the interim government and have the power to overturn its decisions.

But uncertainty over who would attend the conference has exacerbated tensions among Iraq's disparate ethnic, political and religious groups while also raising questions about what effect the final 100-member body would have on the country's future governance. It also remains unclear how the conference would select the council.

The Bush administration is heralding the conference as evidence that its political program for postwar Iraq is succeeding. "The conference will constitute the first opportunity after the transfer of sovereignty for Iraqis from all over the country representing every part of civil society to come together and discuss national issues, and to give their one-month stamp of understanding and approval to the interim government," Secretary of State Colin L. Powell said Thursday in a speech at the U.S. Institute for Peace, a federally funded group.

At the same time, the United States is trying to stay on the sidelines as Iraqis organize the conference. But the effort to show that Iraqis are running the show a month after the handover of political power is stirring deep anxieties about how the process will play out without American expertise.

"We need to stay out of the way. We can counsel, which is why we have an embassy. But we're not going to make these decisions for them," said a senior State Department official who spoke only on the condition of anonymity.

The conference, often compared to the loya jirga in which Afghans chose their interim leadership in 2002, is an important dry run for the even bigger challenge of holding Iraq's national elections by the end of January.

If the conference succeeds, public support for the new government and the elections would likely increase. If it is delayed or perceived as flawed, however, it could alter the timing and credibility of the entire U.S.-brokered political transition, U.S. and Iraqi officials say.

So far, preparations have featured intense lobbying, feisty debates and a bit of chaos, which Iraqi and U.S. officials say is proof of a burgeoning Iraqi political scene. "The big story here is that there is a political process and therefore uncertainty," said Deputy Prime Minister Barham Salih.

But in a sign of how much still has to be sorted out, conference organizers have not yet decided how to pick the 100 council members. U.N. advisers proposed that anyone with 10 votes should win a seat.

A bigger problem is whether all ethnic and religious groups would be fully involved in the conference. Interest has been strong in southern Iraq, which is populated mostly by the Shiite Muslims who account for about 60 percent of Iraq's 25 million people. Brutally repressed by President Saddam Hussein and his Sunni-dominated Baath Party government, the Shiites are eager to move Iraq closer to majority rule. But in the Sunni heartland of central Iraq and in northern areas where ethnic Kurds, Arabs and Turkmens are maneuvering for power, the conference is less popular, Iraqi officials said.

Bringing in the Sunni minority, which was largely on the fringe during the U.S. occupation, is most critical, officials said. Prime Minister Ayad Allawi has said that by drawing as many Sunnis as possible into the conference process, the interim government can fracture a key component of the insurgency.

"Allawi's broader strategy is to co-opt the insurgents without blood on their hands. He and others have made clear that this is a big-tent event and they're not going to try to exclude all extremists," the senior State Department official said.

But key Sunnis say that snags in organizing the conference threaten to create a backlash among cooperative Sunnis. "There are a lot of people not happy about what's going on. There were supposed to be application forms, but they weren't distributed, so many people didn't know how the process was supposed to happen," said Hatem Mukhlis, a former New York doctor who returned from exile after the war.

"There was no effort to explain to the public how to get involved, which has created a lot of confusion about the whole process," he said after returning from a trip to the Sunni Triangle, north and west of Baghdad. U.S. officials have also been concerned about the lack of public outreach.

To prevent a Sunni boycott, Mukhlis said he has been urging those who refused invitations to become candidates to reverse course. U.N. officials are also planning to talk to those boycotting the conference, said Iraqi officials, who remain optimistic about the event.

"We will see uproar and complaints that it was not inclusive enough and so and so was not let in. But we're also getting petitions daily to put in a good word for others to be included," Salih, the deputy prime minister, said. "There is almost too much interest in some places."

In the southern port city of Basra, more than 1,000 people vied for 43 conference seats, and almost 1,300 in Kut sought 22 positions, according to Iraqi officials.

Candidates must meet three criteria, according to Fuad Masoum, head of the preparatory committee. They must have a "good reputation," he said, and not be a former member of either Hussein's security forces or the Baath Party.

The selection process, which began last week, used a complicated formula to come up with 548 delegates from Iraq's 18 provinces, including 130 from Baghdad; 140 from political parties; 70 tribal leaders; 170 intellectuals and prominent Iraqi figures; and 100 from the preparatory committee, Masoum said.

Because the conference could make or break political careers and parties, Iraqi and U.S. officials are also concerned that sparring could leave participants bruised or angry.

Two groups are expected to make big plays for power, they say.

Members of the former U.S.-appointed Governing Council who were bypassed in the formation of the interim government, most notably Iraqi National Congress leader Ahmed Chalabi, are expected to try to make comebacks.

Chalabi has been mobilizing a new Shiite bloc that includes supporters of rebel cleric Moqtada Sadr. Chalabi's goal is to win a seat and ultimately become leader of the council to be formed at the conference, according to Iraqi and U.S. officials.

Religious parties also are seeking greater prominence after U.N. and U.S. envoys excluded them from the interim government. Officials in the Sunni and Kurdish communities say they expect the most intense battles to be fought over how many representatives of religious parties end up on the 100-member body. A council that was heavily religious could reject government decisions and challenge the notion that Iraq must evolve into a secular democracy.

"The Islamists are trying to take over the process big time," said Mukhlis, who charged that they were getting help from predominantly Shiite Iran. The two Shiite groups that have been particularly active are the Dawa party, whose leader, Ibrahim Jafari, won the highest popularity in opinion polls, and the Supreme Council for the Islamic Revolution in Iraq, Iraqis say.

The Bush administration acknowledges that the process has an inherent tension. "We want to encourage dialogue, but we also don't want the process to be so vulnerable to the folks who have opposing views that they can hijack the conference and prevent it from achieving what it was intended it to achieve: support for the political transition, endorsement of the interim government and a means to sponsor reconciliation. The Iraqis don't want this to be a divisive process," said the State Department official.

Looming over the whole process is security. A major attack could seriously undermine public enthusiasm about getting involved in politics, U.S. and Iraqi officials warn.

"We have for a long time been concerned about the security situation and how that is going to affect any large congregation of people in the middle of Baghdad," said Ahmed Fawzi, a U.N. spokesman. "This is being discussed by the preparatory committee, assisted by the U.N.," he said.

Correspondent Rajiv Chandrasekaran contributed to this report.

A police officer wounded in a firefight is rushed to a Baghdad hospital. Officials fear a major attack could curb public enthusiasm for politics.Prime Minister Ayad Allawi said that drawing as many Sunni Muslims as possible into the conference process could help break the continuing insurgency in Iraq. The Sunni minority was largely on the fringe during the U.S. occupation.