A two-strong UN team has arrived in Baghdad to assess the feasibility of the organisation returning after the bomb attack on its HQ there in August.
The UN is edging back into Iraq amid popular demand
Hours earlier UN chief Kofi Annan said he would shortly decide whether the UN's mission in Iraq would be restored.
Staff were pulled out after a bomb killed the UN envoy and 20 others.
The leading cleric of Iraq's Shia Muslim majority has insisted on a UN role in the transfer of political power from the occupying US-led coalition.
A representative of Ayatollah Ali al-Sistani urged his followers on Friday to halt mass protests against US plans for an unelected government pending a UN decision on the issue.
However, he indicated his willingness to compromise if the UN sent a team to assess whether elections could be held.
The two unnamed UN officials - described by the organisation as a military adviser and a security coordinator - were due to have talks with the US-led administration and inspect possible sites for new UN offices, said spokesman Stephane Dujarric in New York.
They are thought to be the first foreign UN staff to visit Iraq since the evacuation and their mission appears to be primarily connected with staff security.
"The opening of a direct line of communication with the coalition on security matters is necessary for the planning for the safety and security of UN personnel... and for
an eventual return of UN international staff to Iraq," said Mr Dujarric.
Coalition forces were guaranteeing the team's safety, he added.
The spokesman stressed that a separate security assessment would be needed if Secretary-General Annan decided to send an election mission.
Speaking earlier on Friday at the World Economic Forum in Davos,
Mr Annan said he would "shortly" announce his decision.
Ayatollah Sistani insisted that the only legitimate government in Iraq would be one elected by the Iraqi people.
Tens of thousands demonstrated after Sistani's call for early polls
But in his latest comments, he was quoted by a representative as saying that no protests should be held until the UN position had become clear.
"After that, we will say our word," his spokesman said.
The BBC's Middle East analyst, Roger Hardy, says that after three and a half decades of dictatorship, the idea of full and free elections has an obvious appeal - especially to the majority Shia, who have long felt excluded from power.
He says that in the face of the ayatollah's stubborn opposition to an unelected government, everyone is being forced to reconsider the options.
At issue is how to choose the 250 Iraqis who will comprise a body known as the transitional national assembly.
In June - according to the timetable the Americans have proposed - that assembly will select an Iraqi government which will take power from the current US-led administration.
The ayatollah says the assembly's members must be elected. The US says that is not feasible and the assembly should be chosen through a series of local meetings in each of Iraq's 18 provinces.
All sides agree that the handover of power must take place by 1 July.