The Soviet Union, acting in mirror fashion to the United States in Somalia, is reported here to be seeking wider access to Ethiopian military facilities, particularly for its Navy. But like its chief superpower rival, Moscow is having difficulty in getting all it wants from its main ally here in the Horn of Africa.

Despite its increasingly close ties with the Eastern Bloc, Ethiopia has heretofore been reluctant to allow a high Soviet military profile to develop on its soil.

Ethiopia is linked to Moscow by a 20-year treaty of friendship and cooperation and is probably its most important ally on this continent by virtue of its strategic location on the Red Sea. The Soviets have provided this country with around $1.5 billion in military assistance in the last three years, the largest such commitment they have ever made to a black African state.

In return, the Ethiopians have allowed Moscow to establish a relatively obscure anchorage for its Indian Ocean-bound warships in the barren Dahlak Islands off the northern Ethiopian port of Massawa, according to Western intelligence sources. But the Soviets are said to be pressing the Ethiopians now for better onshore facilities as well as the construction of airfields for use by its and Ethiopia's air forces.

In so doing, Moscow is seen here as reacting partly to the American military building in the Indian Ocean and Persian Gulf region and partly in accordance with the superpower assumption that bases or facilities are the quid pro guo for arms in this strategic region of the world.

Ethiopia's military leader, Lt. Col. Mengistu Haile Mariam, returned from a two-week stay in the Soviet Union in early November during which he discussed with Kremlin leaders ways of "deepening and expanding" their relations in all fields, according to the joint communique issued at the end of his state visit.

During his sojourn there, Soviet part leader Leonid Brezhnev hailed the "new dimensions" he said were being added to every article of the Soviet-Ethiopian friendship treaty and said relations between the two countries were taking on "an internationalist character," a possible reference to Ethiopian cooperation in the military field.

Included in the 70-member delegation Mengistu took with him were high-ranking military officers led by the defense minister, Brig. Gen. Gesfaye Gebre-Kidan, who was reported in the press here to have held separate talks with Soviet military leaders. There was no indication, however, what they discussed or whether any agreement was reached on further Soviet arms deliveries to Ethiopia or increased access for the Soviets to Ethiopian military facilities.

Last month, Ethiopian Foreign Minister Feleke Gelde Giorgis vehemently denied in an interview that there was any military "base" for the Soviet Union or any other country in Ethiopia at that time and said all foreign bases in Africa should be closed down.

While Feleke may have been obfuscating the issue by making a U.S.-government style distinction between a base and a facility, his remarks nonetheless reflect what is believed by Western observers here to be a considerable Ethiopian reluctance to become more deeply involved in the Soviet-American military competition for a foothold in the strategic Horn of Africa.

Furthermore, the Ethiopians have launched a major diplomatic campaign to dissuade the United States from going ahead with its plan to provide arms to Somalia in return for access to Somali ports and airfields, convinced that the American commitment will embolden the Somalis in their struggle to annex the Ogaden.

Thus the Ethiopian government would seem to have little interest in provoking Washington at this stage by giving into Soviet pressure for a larger miliatry presence in this Red Sea nation.

Western diplomatic sources here and in Washington say the Ethiopians have turned down several Soviet-proposed military construction projects on the ground that they could not afford the cost. But the American plan to turn Somalia into a springboard for its Rapid Deployment Force has increased the Soviet interest in obtaining wider access to Ethiopia as a counterpoint.

In early July, Sergei Gorshkov, Soviet deputy defense minister and admiral of the fleet, paid a six-day "working visit" to Ethiopia. The local press said he visited civilian and military establishments in the Red Sea province of Eritrea, including the main port of Massawa, and discussed "bilateral cooperation" with Ethiopian authorities.

There was no indication whether he also visited the Dahlak islands, an archipelago of mostly tiny islets devoid of any buildings except the remains of some Italian World War II fortifications and inhabited by only a few hundred people, most of them partially from deep-sea coral diving.

While one high-ranking Ethiopian official has said there is no new construction on the islands, some diplomatic sources here say the Soviets are using them as a open-air depot and have towed the floating dock that once serviced their ships at Berbera, Somalia, to the Dahlaks.

The Ethiopian government has not commented on a New York Times report that the Soviet Navy has stepped up the use of the Dahlak island since the onset of the Iranian-Iraqi war, anchoring half its Indian Ocean fleet there in mid-October.

The Ethiopians are in a difficult position to reject Soviet entreaties for the expanded use of their facilities, since they are totally dependent on Soviet arms and feel a large debt of gratitude for the crucial assistance Moscow gave to them in 1977 when the country was seriously threatened with disintegration because of the separatist wars in the Ogaden and northern Eritrea and mounting internal opposition.

Moscow extended a $2-billion line of credit to the Ethiopians for the purchase of arms and rushed a massive amount of war material to this country in an airlift that impressed Western military analysts as well as the Mengistu government.

Furthermore, as a nation formally committed to becoming a socialist and communist state, Ethiopia views the Soviet Union as a natural ally and shares its views on most foreign policy issues. In addition, it feels surrounded by U.S.-backed enemies, some of which, such as Egypt and Saudi Arabia, have been providing arms to Somalia for the Ogaden war.

So long as the struggle over the Ogaden and Eritrea continue, Ethiopia is certain to remain highly dependent on the Soviets and thus vulnerable to their requests for wider access to ports and airfields.

This may help to explain the unusually strong Ethiopian reaction to the American plan to provide arms to Somalia and to establish facilities for the U.S. Rapid Deployment Force, although the main concern here remains their impact in encouraging Somalia to continue the Ogaden war.

"The American decision to take over Berbera [a port in northern Somalia] is an act that whether by design or not is bound to put a lot of pressure on Ethiopia by way of countering such a provocative action taken by the Somali and American governments," said Negussay Ayele, head of the political science department at Addis Ababa University.

"One should only think back to 1975 to review what the American reaction was to the first news of a Soviet base in Berbera," he continued. "Would people expect the Ethiopians to react with any other response, especially given the fact that Ethiopia has just been scorched by the biggest and bloodiest war in the continent, the war of Somali aggression in the Ogaden in 1977?"