The United States yesterday issued an urgent appeal to both Ethiopia and antigovernment rebels to allow the United Nations and western private voluntary groups to safely transport aid to millions of people again facing famine in northern Ethiopia.

The U.S. appeal for both sides to adopt "an open-road, own-risk" policy came as the Ethiopian authorities yesterday closed down the main road for transporting vital relief supplies from the city of Asmara in northern Eritrea south to Mekele, one of the regions worst affected by the drought.

"We don't know how long the roads will be closed, but they are the lifeline to providing food for people," said Julia V. Taft, director of the U.S. Agency for International Development's (AID) disaster relief office. She has just returned from a four-day visit to Ethiopia.

"We're very adamant, as are all the donors, in pleading with the government and the rebels to let the food flow," she said. Taft urged both sides to assure safe passage for relief convoys and accept a cease-fire in their war to allow emergency food distribution.

It was on the Asmara-to-Mekele road that Eritrean rebels attacked and burned a convoy of 23 trucks carrying 450 tons of relief food supplies on Oct. 23. The attack shocked the international community and raised what Taft called "an enormously important new dimension" to efforts to supply food to "over 5 million people" facing what AID is calling a drought "as serious or even more serious" than one in 1984-85.

Taft indicated that AID does not believe Ethiopia is doing enough to avert another famine disaster.

"This is not a situation where there is a lack of resources from the donors available. . . . . There is a lack of political will on the part of the combatants in this 25-year-old struggle to provide the necessary safe passage, which we call open road, own risk," she said. " . . . The security issue is the one that is driving the famine concerns that face us," she added.

Taft said there are sufficient relief supplies in Ethiopia's main ports and towns as well as trucks to transport them. But the security situation was such, she said, that both foreign relief and private food-laden trucks either were being blocked by the government, or their drivers were afraid to travel after the Oct. 23 attack.

Only two relief convoys had moved since then, she said. Two other rebel attacks took place last week in the same area, one on a military convoy carrying needed fuel supplies and the other on private truckers, she added.

Taft said foreign donors and relief groups were also pressing the Ethiopian government to give higher priority to the looming famine and mobilize its own resources, including trucks. Otherwise, she warned, the experience of the 1984-85 famine will recur, when large amounts of relief supplies reached ports and major cities but could not be distributed to the interior in time to save hundreds of thousands of people.

Taft made it clear the U.S. government, in making its appeal, was seeking to mobilize international pressure on both the Ethiopian government and the rebel group responsible for the Oct. 23 attack "to recognize it is their people at risk."

The Eritrean People's Liberation Front has asserted responsibility for the attack, saying three of the convoy's trucks carried arms and ammunition.

Taft said the United Nations and other private relief groups in Ethiopia had decided they did not want the Ethiopian government to try to provide military escorts for the relief convoys. Instead, she said, they wanted the government "to step aside" and keep the roads open so that the United Nations and private groups could act on their own.