WASHINGTON » The Obama administration is encouraging a major new power-sharing arrangement in Iraq that could retain Nouri al-Maliki as prime minister but in a coalition that would significantly curb his authority.

The compromise plan was promoted in Baghdad last week by Vice President Joe Biden, though at a time when American influence is waning and the United States continues to draw down troops. The new plan would alter the structure of Iraq’s government by bringing additional restraints to the authority of Iraq’s prime minister and establishing a new committee with authority to approve military appointments, review the budget and shape security policy.

U.S. officials said that the approach, which aims to bring al-Maliki’s State of Law party, Ayad Allawi’s Iraqiya party and the Kurdish alliance into a governing coalition, represents the best chance to break the political logjam that has left the Iraqi public without a new government six months after voters went to the polls.

A senior U.S. official said that the plan was likely to result in a new government over the next month or so, and that Secretary of State Hillary Rodham Clinton could travel to Baghdad at that time.

"We don’t really see what other option there is out there," said another U.S. official, who asked not to be identified because he was discussing confidential negotiations. "If we have a national unity government that is less efficient but perceived as representative and accountable to the Iraqi people, we think that’s better for the future of Iraq."

American officials assert that they do not have a preferred candidate for prime minister. But the proposal is intended to make al-Maliki, or a strong-willed successor, more palatable to the rest of a broad-based governing coalition. The redefined authority would be codified by new legislation but would not require that the Constitution be amended.

Doubts remain whether the Americans can close the deal and, meanwhile, Iran has stepped up its efforts to press an alternative coalition in which al-Maliki might remain prime minister but in a coalition with his Shiite rivals and not Allawi. Which coalition prevails will serve as a barometer on whether Iran or the United States has more prestige in an unsettled and still turbulent country.

An utter lack of trust among the contending factions has hampered all efforts to build a coalition. Some experts say that even if the U.S. proposal succeeds it could leave Iraq with a government that, by being so broad-based, is too weak to tackle the tough problems that lie ahead.

"It may perhaps help smooth the surface in the very short run, but it isn’t a good solution for Iraq as a viable state in the long run," said Reidar Visser, an Iraq analyst.

Politics in Baghdad have been stymied as insurgents have continued bombings and assassinations and Iraqis have become increasingly disgruntled about the failure of the government to deliver basic services.

Though turnout for the March parliamentary election was relatively high, the vote failed to produce a decisive outcome. The Iraqiya party, which is headed by Allawi, a secular Shiite, but represents many Sunnis, won 91 seats. Al-Maliki’s State of Law secured 89 seats, while the Iraqi National Alliance, a Shiite coalition, won 70 seats.

Across the spectrum, there are concerns that al-Maliki’s return would further strengthen the hold of his Dawa Party over the key instruments of the state — the police, the army and, perhaps most important, intelligence — and close off the possibility that there will ever be a peaceful transfer of power to a rival party.

Biden said in an interview in Baghdad last week that if Iraq went another six months without a new government it would raise concerns that Iraq’s military might intervene in politics. "My worry will be that generals in the military will start saying, ‘Wait a minute, which way is this going to go?"’ he said.

"But I think we are far from that," said Biden, who added that the Obama administration had been striving for a political breakthrough. "We have been deeply involved with each of the parties from the day after the election results came in," he said, adding, "This has been constant."

The idea of a new power-sharing arrangement has been discussed for several months. Soon after the election results were certified in June, Christopher R. Hill, the U.S. ambassador in Baghdad at the time, and his political aides drafted a paper in consultation with Biden reflecting ideas discussed among Iraqi politicians.

The aim was not just to curb the powers of the prime minister, but to create new positions that could be occupied by members of a broad governing coalition. Toward this end, a largely advisory Iraqi government body — the Political Council for National Security — would be given the power to review security, budget and oil export policy.

"I think there is a growing awareness that there is a need for something akin to our National Security Council," said Biden, who noted that such a step would be taken "to sort of balance the powers, but also provide landing spots for the number of serious people who have to occupy serious ministries."

American officials assert they are not trying to pick who should run the government but rather to shape an arrangement conducive to compromise.

Still, current and former U.S. officials said that a number of specific possibilities had been discussed with the Iraqis, including having Allawi lead the new committee or having him serve as president with clearly defined veto authority, a position occupied by Jalal Talabani, a Kurdish leader thought to be reluctant to give up the job.

According to one early variation of the plan, the new committee would be headed by a secretary-general and would include the prime minister and the president.

Other members of the panel could include the head of the judiciary and the head of Kurdistan’s regional government as well as members of some powerful ministries. Some of al-Maliki’s authority over security would be shifted to the new committee, but he would retain his role as the commander in chief of Iraq’s armed forces.

While it appears publicly that there has been little progress, behind the scenes both sides have prepared competing papers on how the new body would function. Difficult issues remain, however, hindered by the poor chemistry between al-Maliki and Allawi.

"We have made slight progress," Allawi said in an interview, "and I emphasize the word ‘slight."’

Discussing the new committee, Allawi insisted that it must have executive power, a budget, advisers and the right to call ministers to testify, effectively making it a position whose influence would compete with the prime minister’s.

"If there were powers, and there was clarity, and there was an explanation why we should not be able to form a government, then why not, to serve the country?" Allawi said.

In contrast, al-Maliki appears to be guarding his prerogatives on the assumption that he can remain prime minister. A senior Western diplomat said that al-Maliki believed that the shifting of his power to the committee should be "events based," or curbed according to the security situation in the country.

One point of disagreement in the talks is the fate of about 140 appointments by al-Maliki to senior positions in the military and intelligence. Allawi said he had insisted that those appointments be reviewed and perhaps overturned, by the council or parliament; al-Maliki’s allies have said only that they should be "assessed."