UN diplomats said Secretary-General Kofi Annan decided on the move on Tuesday.
But Security Council envoys doubted the world body would send substantial numbers of political staff to Baghdad before 30 June when a provisional government is due to take power.
The envoys said Kieran Prendergast, the UN undersecretary-general for political affairs, had sent a letter to US Ambassador John Negroponte, saying a four-member team would soon be dispatched.
"The return to Iraq of United Nations international staff is contingent in part on acquiring and upgrading suitable working and living accommodations and enhancing security arrangements," Prendergast said in the letter.
The UN pulled all its international staff out of Iraq in late October after a bombing of its headquarters in Baghdad, which killed 22 staff and visitors including UN mission chief Sergio Vieira de Mello.
Since then, the Secretary-General has been hesitant to send back any international staff, on both safety and political grounds.
The small security team to be dispatched is to provide extra support to Iraqi national staff, supervise needed security improvements and work with the US-led occupation authorities.
There are about 1000 Iraqi staff working for the UN in Iraq, helping with relief efforts.