WASHINGTON (AP) _ The State Department expressed outrage Monday over the destruction by an Ethiopian rebel group of 23 relief trucks carrying almost 450 tons of emergency food to a drought-stricken area in northern Ethiopia.

The convoy consisted of 16 United Nations trucks carrying about 350 tons of food and seven trucks belonging to Catholic Relief Services with another 94 tons, department spokesman Charles Redman said.

''We deplore this outrageous action which targeted trucks clearly marked with the United Nations insignia and whose humanitarian mission is well and widely known by all persons in Ethiopia,'' Redman said.

The attack took place in Eritrea province, one of the areas which was the hardest hit by a summer drought that, according to U.S. estimates, has affected between 3 million and 5 million Ethiopians.

Eritrea is believed to have lost its entire main season cereal crop.

Redman said the attack last Friday was apparently carried out by secessionist rebels in Eritrea province who have been fighting the country's Marxist government. It was not clear which rebel faction was responsible, Redman said.

On Capitol Hill, Rop. Mickey Leland, D-Texas, chairman of the House Select Committee on Hunger, said a spokesman for the Eritrean People's Liberation Front had called his office claiming responsibility for the attack and attempting to explain it.

''We made it clear that there is no explanation, no excuse, for actions which directly threaten the lives of thousands of innocent people,'' Leland said in a statement.

A Leland aide, Jeffrey Clark, said EPLF spokesman Tesfai Ghermazien told him that the rebels had attacked the convoy because it was traveling through a tense region where a major battle had taken place five days earlier, and rebel troops suspected the trucks were carrying arms.

Clark said the EPLF official told him that there were 34 trucks in the convoy and that three carried military equipment, an assertion denied by State Department, United Nations and relief officials.

Redman urged all parties to the conflict in Ethiopia to avoid interference with emergency food shipments.

Private voluntary groups in contact with the rebel groups will be approached to convey U.S. condemnation of the attack, Redman said. During the 1984-86 drought, he said the rebels recognized the humanitarian nature of the U.S. relief effort and generally abstained from attacking or harassing relief vehicles and personnel.

If this practice is not resumed, he said, ''relief programs could be severely interrupted with dire human consequences in these regions.''

The U.N. trucks and two of the Catholic Relief Services vehicles had been purchased with U.S. government funds. The U.N. vehicles were carrying grain provided by the World Food Program while the CRS trucks were delivering U.S.-supplied grain.

Last month, the United States approved a request for 115,000 metric tons of emergency food commodities to help combat the threat of renewed famine.