NAIROBI, KENYA, OCT. 25 -- In a rebel attack that a senior U.N. official today said has "horrific implications" for famine relief in Ethiopia, a large convoy of donated trucks carrying western food aid has been ambushed and burned.

The convoy, traveling in northern Ethiopia without military escort, was stopped Friday by rebel soldiers who doused 23 trucks with gasoline and set them afire, according to relief officials in Ethiopia. They said one driver was shot and killed by the rebels.

Nearly 450 tons of wheat, enough to feed 45,000 people for a month, were destroyed, officials said. In addition, they said that all 23 trucks, most of which were late-model, long-haul vehicles with a combined replacement value of more than $2 million, were destroyed.

The wheat was a gift from the U.N. World Food Program and the U.S. government. The trucks were gifts from Band Aid, a British relief agency, and Catholic Relief Services, an agency based in the United States.

The attack came at a time when the United Nations and western donors are attempting to rush emergency food aid into northern Ethiopia, where severe drought threatens nearly a million people with starvation.

Relief agencies have warned that if large amounts of food aid do not reach distribution centers in Eritrea and Tigray by December, there will be a mass migration of destitute people into makeshift camps. It was in similar camps in 1984 and 1985 that hundreds of thousands of Ethiopians died, primarily from infectious diseases.

"This raid has consequences far beyond the immediate loss of food and trucks," said David Morton, director of operations for the World Food Program in Ethiopia, contacted today in Addis Ababa, the Ethiopian capital. "It raises questions about the future movement of any relief food in the north. For Eritrea and Tigray, the attack has horrific implications."

The attack, Morton said, comes as the United Nations is "appealing to the donor community for logistical support in transporting food."

Rebels in Eritrea, a former Italian colony that was formally incorporated into Ethiopia in 1962, have fought for autonomy for the past 27 years. The conflict is the longest continuously running civil war in the world.

October is the traditional month for a government offensive against the rebels and fighting in the region has been intense in recent weeks.

The British Broadcasting Corp. reported today that an Eritrean rebel group called the Popular Liberation Front claimed responsibility for the raid. The BBC quoted the rebel group as saying the attack was staged to disperse enemy forces escorting the convoy.

The Popular Liberation Front is one of several rebel groups fighting in Eritrea. The largest such group is the Eritrean People's Liberation Front, which in the past has allowed free passage of relief convoys.

Morton and other relief officials contacted today in the Ethiopian capital insisted that the convoy was not escorted by the Ethiopian military. "If the rebels were going for a military target, why did they burn the trucks and the food?" Morton asked.

A report early this month by a multidonor committee on relief transport said that 300 additional long-haul trucks were needed to deliver the 400,000 tons of relief food required in Eritrea and Tigray next year. The World Food Program had only 40 trucks in the north before Friday's raid.

The convoy was attacked while traveling south from Asmara, the capital of Eritrea, toward the Tigrayan city of Adigrat.

Officials said the attack occurred 30 miles from Asmara on a road where rebels in recent years have allowed free passage of relief convoys.

The food destroyed on Friday was intended for Tigrayan drought victims who live near the city of Mekelle, where there has been a nearly total crop failure in recent months.

Relief officials said they were relying on trucks to deliver most of the relief food needed in Tigray and Eritrea.

But Morton said today that the rebel raid increases the likelihood that much of the food may have to be transported by air, at more than double the $140-a-ton cost of delivery by truck.

The Ethiopian government in September appealed to western donors for nearly one million tons of food for the expected shortage in 1988. Morton said today, "It seems possible that that amount of food can be raised. The problem has always been: can that food be moved into the right areas? This incident puts a whole new light on the problem."