The draft UN Security Council resolution prepares the ground for a future US and UN deployment in the West African country.
It would give a UN mandate to West African troops or those from other countries to go to Liberia immediately.
It would also pave the way for a UN peacekeeping operation to take over in October.
The draft resolution calls on Secretary-General Kofi Annan to deploy troops by October 1.
It also approves an urgent request from Annan for the United Nations to underwrite some of the costs of sending Nigerian peacekeepers to the country.
Annan told a news conference on Wednesday that he expected the West African peacekeeping force ECOWAS to "tell him soon" when it would deploy Nigerian forces.
But President George W Bush would not say whether he would commit ground troops to Liberia, although two warships with US Marines are en route.
The UN will authorize a Liberian
peacekeeping force by October 1
He repeated that Liberian President Charles Taylor must step down and a cease-fire must take hold before any Americans would go in to stabilize the country.
Meanwhile, Annan said the peacekeeping operation was an urgent priority.
"This is one of those rare situations that even though the cease-fire has broken down, both sides genuinely seem to want the international force to come in, not just the government and the rebels but also the population," he said.
US under pressure
Nigeria has said it will send 1,400 troops to Liberia, starting with a 750-strong battalion.
The United Nations wants the Nigerian battalion to go in first, followed by the United States and another Nigerian battalion that would include troops from other West African nations.
The United States has been under growing pressure to intervene in Liberia, founded by freed American slaves in 1847.