ADDIS ABABA, ETHIOPIA, NOV. 14 -- A senior American official said here today that the government of Ethiopian President Mengistu Haile Mariam appears willing to revive stalled peace talks with Eritrean separatists under U.S. auspices and to allow relief shipments into the rebel-held Red Sea port of Massawa. He called on Eritrean rebels to "reciprocate" the cooperation.

"I was very pleased in my discussions with the foreign minister {Tesfaye Dinka} and the president to learn that there is a continuing commitment to a peace process," said Herman J. Cohen, assistant secretary of state for African affairs, in a statement to reporters after a three-hour meeting with Mengistu. "We are very pleased to be able to contribute to that."

No date has been set for renewed negotiations to end the long and bloody struggle over the status of Ethiopia's northernmost province of Eritrea. Cohen said he expected the talks to resume "in the near future."

Cohen's overnight stop in the Ethiopian capital was part of intensified efforts by the American government to mediate and put an end to the 30-year-old conflict. Observers say the two sides, which broke off talks almost a year ago, have become more receptive to the prospects of peace because of mounting pressures from an ever increasing drain on human and financial resources.

The high-level U.S.-Ethiopian meeting also drew attention to the slow but steady warming between Washington and its formerly hard-line Marxist antagonist -- a product not only of Ethiopia's support for the United States in its confrontation with Iraq, but also of recent modifications in the Mengistu government's strict socialist policies and some halting steps on human-rights issues.

In addition, diplomatic observers say pragmatists within the Ethiopian government have realized the benefit of stronger U.S. ties, given dwindling Soviet support and the prolonged struggle with two major insurgencies -- the Eritreans and rebels in the northern province of Tigray.

Two high-ranking American officials, Robert C. Frasure, director of African Affairs at the National Security Council, and John Davison, the State Department's office director for East Africa, visited here a week ago to pave the way for Cohen's visit and to follow up on informal talks that brought together the Ethiopian government with Eritrean and U.S. officials in Washington Oct. 4.

Cohen said he was happy with the Ethiopian government's continued economic changes and its plans to allow "reunification of separated families," a term used primarily in reference to thousands of Ethiopian Jews waiting to emigrate to Israel.

"On the whole, I feel that U.S.-Ethiopian relations continue to improve," Cohen said.

Cohen also found the Ethiopian government "essentially prepared to work with the United Nations" to permit relief workers and supplies into the port of Massawa, which was captured by rebels of the Eritrean People's Liberation Front in February. The port was bombed and shelled heavily by the government after it fell, and the EPLF has reported sporadic bombings ever since.

Cohen indicated that he believed the Eritrean side was the recalcitrant party in American mediation efforts, although he allowed that communication among Eritrean guerrilla leaders was "difficult" for logistical and other reasons, and thus might have delayed an EPLF response.

He said he was "very disappointed" that the Eritreans had so far rejected U.N. efforts to send a team into Massawa to evaluate damage to the port in advance of any renewal of food shipments, and he urged them to "work with the United Nations." Last July, a U.N. ship with four technicians aboard was turned away from Massawa after it insisted on communicating only with the "sovereign power," namely Addis Ababa.

"I believe the Ethiopian government has effectively shown great flexibility in recent weeks," Cohen said, "and I would ask the EPLF to reciprocate."

Opening Massawa to relief aid would vastly improve the outlook for an estimated 4 million people in northern Ethiopia facing a new of famine of potentially catastrophic proportions.

The existing airlift to the besieged Eritrean capital of Asmara is extremely costly, as is the long and complex process of trucking supplies into northern territory held by Tigrayan rebels along the so-called southern line. Moving relief over the border from Sudan poses political problems and is subject to government attack.

Talks between the EPLF and the government, mediated by former president Jimmy Carter, broke down in December 1989 after the Ethiopian government refused an Eritrean request to allow a U.N. observer to participate in the discussion.