"The US role will be limited in time and scope as multinational forces under the United Nations assume the responsibility for peacekeeping," White House spokesman Scott McClellan said in a written statement.
The US will also help arrange a political transition in Liberia, McClellan added.
Meanwhile, mortar shells on Friday rained down in Monrovia as government forces and rebels continued to fight pitched battles for control of the country's scarred capital.
More civilian deaths
A reporter with the French news agency AFP said at least 11 civilians were killed in attacks on the diplomatic quarter of the city.
Located in the same Mamba Point neighbourhood, the US embassy was also hit by at least two mortar shells.
"I don’t have money to buy food. See my children, they are hungry, they have not eaten for a day"
Discussions between the US and other West African countries, principally Nigeria, over what shape an intervention should take, have delayed action.
In the meantime, Liberia has slipped into total anarchy.
"We don't want to get there and make a lot of mistakes," General Martin Luther Agwai, chief of staff of the Nigerian
army, told reporters.
"We want to make sure that everything is done right so that once we get there, we deliver."
The Economic Community of West African States agreed at a meeting in Senegal on 23 July to send a contingent of Nigerian forces to restore order in the capital.
Two battalions of Nigerian troops are on standby, though they will not likely be given the order to enter Liberia for another few days.
African leaders are due to meet again in Ghana on Monday to finalise the deployment.
Drinking water in the city is now scarce and food supplies are dwindling rapidly.
The city’s main water plant has been out of operation for days. People are currently relying on wells, many of which have not been chlorinated.
“I don’t have money to buy food. See my children, they are hungry, they have not eaten for a day,” wailed out-of-work housewife, Esther Fahnbulleh.
“Let anyone come to bring peace to this country and come now,” she said.
Rebels of the Liberians United for Reconciliation and Democracy (LURD) have been battling government forces to oust President Taylor.
Taylor is refusing to leave before the arrival of peacekeepers, despite having agreed earlier to step down and seek asylum in Nigeria.