Said Djinnit, peace and security commissioner for the African Union, made the announcement on Monday after a meeting with officials from the United Nations and the European Union.
The Inter-Governmental Authority on Development (IGAD), grouping seven east African countries, is planning to dispatch such a force. However, it has run into problems including the existing UN arms embargo on Somalia and opposition from the Islamic Courts militia which has recently emerged as a powerful player.
Djinnit said: "We have agreed to send an assessment mission that will assess all that is required for the peace-supporting mission and check the situation on the ground.
"Meanwhile the planning should start."
He said the mission should go as soon as possible.
He said the current situation, following the Islamic Courts militia's defeat of a US-backed alliance of local commanders in Mogadishu, offered the opportunity to restart talks and the peace process.
Tim Clarke, the European Commission's representative in Ethiopia, said: "We have reached a consensus to send an assessment team to Somalia very soon led by the AU and IGAD."
IGAD groups Djibouti, Eritrea, Ethiopia, Kenya, Sudan, Uganda and Somalia's interim government.
"The very important element now is to have dialogue as urgently as possible to find a way out of this situation."
"The federal transition government is the only frame to start this dialogue"
Mohamed Ali Foum,
AU envoy to Somalia
Mohamed Ali Foum, the AU's envoy to Somalia, said the team could go as early as next week.
"We are calling for dialogue to be held between the federal transition government and the parties," he said.
"The federal transition government is the only frame to start this dialogue."
The gathering was attended by members of AU's executive body, the commission, representatives of the seven-nation Intergovernmental Authority on Development that leads peace efforts on Somalia and UN, European Union, British, Swedish, Italian diplomats.
The meeting in the Ethiopian capital follows an international meeting the United States convened last week in New York after victories for the Islamic Courts militia.
That meeting concluded with the US-organised group of nations lending its support to Somalia's transitional government and demanding unfettered access so aid groups can help Somalia's impoverished people.