MOGADISHU, Somalia - Ethiopian troops who played a crucial role in helping Somalia's government drive out a radical Islamic militia began withdrawing yesterday, raising fears of a power vacuum unless peacekeepers arrive soon in this chaotic nation.

Somalian government spokesman Abdirahman Dinari said Ethiopia had helped chase out the Council of Islamic Courts militia, which had taken over the capital and much of southern Somalia. But he said it was time for the neighboring forces to leave.

"As of today," he said, "the Ethiopian troops have started to withdraw from Somalia. We are grateful that they played an important role in the restoration of law and order in the country."

Ethiopia's government spokesman, Zemedkun Tekle, confirmed the pullout but gave no details.

The intervention of Ethiopia last month enabled a military advance that proved a stunning turnaround for Somalia's two-year-old government. Without Ethiopia's tanks and fighter jets, the administration could barely assert control outside one southern town and could not enter the capital, Mogadishu.

The potential for violence remains great because of clan rivalries, resentment of the government's Ethiopian backers, and a threat of guerrilla war waged by remnants of the Islamic movement.

Nearly 200 people gathered at the former National University in Mogadishu, cheering as the Ethiopians moved out on trucks and tanks.

"Leave us alone and let us solve our problems," the crowd chanted.

The withdrawal gave a sense of urgency to the arrival of a proposed African peacekeeping force. The African Union has approved a plan to send about 8,000 peacekeepers for a six-month mission that eventually would be taken over by the United Nations.