In endorsing the US position on Thursday, Annan also told reporters that the 30 June date Washington had fixed for a transfer of sovereignty "must be respected".
The White House had asked the UN to come up with proposals for Iraq's political future after the country's Shia leaders rebelled against the original US plans and called for early direct elections.
Annan's announcement came hours after a roadside bomb killed two US soldiers and an Iraqi west of Baghdad in the latest of a series of attacks that have made February the bloodiest month in Iraq since the war.
After a meeting with 46 interested ambassadors, he said he was not yet able to propose who should form a caretaker government on 30 June to run Iraq until elections could be held.
Uncertainty amidst violence
Uncertainty over Iraq's political future is set against the backdrop of relentless violence that has killed scores of US troops and their Iraqi allies who are supposed to take over security.
Iraqis continue to be wounded or
killed in attacks
Annan spoke briefly to reporters between meetings with his senior envoy, Lakhdar Brahimi, who had returned from a series of meetings in Iraq and was making recommendations to the
Choosing a caretaker government will be sensitive.
Iraq's Shia, who have been pressing for early direct elections, will make strong demands. The Sunnis, whose privileges disappeared when Saddam Hussein was toppled in April, fear being marginalised. The Kurds are pushing for autonomy and want a federal state.
No change in handover date
Iraq's US administrator, Paul Bremer, told a news conference in Baghdad that there were dozens of proposals on Iraq's interim government under discussion but that the 30 June handover date would not change.
"There are literally dozens of ways to carry out this very complicated task," Bremer said.
The original US proposal of caucuses in 18 provinces has been discredited by Iraqis and is no longer being pushed by Washington, diplomats at the UN said.
The 30 June deadline is important to the Bush administration before the US presidential election in November as it struggles to hold back violence by insurgent groups.
An Iraqi Shia official said it was acceptable to delay elections by up to three months beyond the handover of power by the US-led occupation administration.
"There is no problem for any transitional body to assume power and prepare for elections on condition that it will be held before October 1, 2004," Ahmad Shakir al-Barrak, a member of the Governing Council, told reporters after talks with Ayat Allah Ali al-Sistani in the holy Shia city of Najaf.
Sistani, the top religious authority for Iraq's Shia, had led the call for elections to be held before the handover.
Duration of Iraq 'stay' unknown
Meanwhile US officials are unsure how long US forces will remain in Iraq
Citing the complexity of creating a democracy, General Richard Myers said on Thursday that planning was underway for two or more rotations of US troops in Iraq.
Myers (R) is unsure how long US
troops will remain in Iraq
"We are planning what we think is worst case for the next rotation and the one after that where we can see how the forces line out," he told reporters.
The estimated 115,000 US troops in Iraq are in the midst of being swapped out for a slightly smaller force.
Pressed to estimate how long a sizeable US force will need to stay in Iraq, he said, "I really do believe that is not knowable."
"If I gave it a good professional estimate, then that would be a standard that people would point to. And knowing we can't know it perfectly, we'd just get hammered," he said.
"Think about how complex this is, trying to turn a country that has not experienced democracy into some sort of democracy, combined to that a place that is inherently violent," he said.
He and his top commanders could "draw out a pretty good diagram about where we think this is going to go," he said. "We think about that. We have thoughts or notions. But I don't think it is safe to say it."
Training and equipping Iraqi security forces to assume the primary security role will be a major focus of US efforts, he said.
"It's never the intention of the US military to leave the Iraqi forces out there on the end of a limb," he said. "We're training these folks, we're mentoring them. We're going to have Americans with the major units for a long time to come."
"This not a cut-and-run sort of thing at all," he said.