An unusual emotional bond between the aging conservatives who run the Kremlin and young Marxist revolutionaries who seized power in Ethiopia two years ago may be part of the reason the Soviet Union risked its painstakingly acquired foothold in strategic Somalia to back the new government in Addis Ababa.

This explanation was advanced seriously today by informed Western sources who have spent much time in recent months analyzing Soviet moves in the Horn of Africa. These sources suggested that the elderly Soviet leadership was stongly attracted to the revolutionary zeal of Ethiopian leader Mangistu Haile Meriam and his followers.

In addition, these sources said, the Soviets firmly believe that the Ethiopian military dictatorship is truly a Marxist-Leninist government, in contrast to Somalia. The Soviets see Somalia as essentially a one-man rule by Mohamed Said Barre, who espoused Communist dogma as an expedient to coax arms and economic aid from Moscow.

The sources suggest that when Mengistu topped Ethiopian Emperor Haile Selassie, the Soviets concluded that they had found a new government in the important northeast section of Africa with which it could feel far more comfortable.

"From Mengistu's first visits, (Soviet Foreign Minister Andrei A.) Gromyko referred to them as 'young revolutionaries for whom the Soviets would do much,'" One source said today.

This person said Gromyko's remarks, unreported in the official Soviet press, have been repeated by other Soviet officials as an indication of the depth of feeling within the Kremlin for Etheopian rulers.

Soviet backing of Ethiopia in the form of military and economic aid was caused partly by Mengistu's anti-American stance. The u.S. role as long-time supplier of arms and money to Etheopia was ended last Asptil.

"The Soviet were rubbing the Americans in it a little when they moved into Ethiopia," a source observed.

Meanwhile, the Soviet government acknowledged for the first time today that its adviser,500, had been ordered out by the Somalis. The Kremlin, in an official four-paragraph dispatch on Tass, the government news agency, declared: "The Somali government took its action unilaterally and in inconditions of war it unleashed against Ethiopia." It described Somalia as "dissatisfied because the Soviet Union did not support Somalis's territorial claims and refused to facilitate the stirring of fratricidal war in the Horn of Africa . . . Judging from the present steps, chauvinist expansionist moods prevailed over common sense inside the Somali government . . . "

He Somalis have taken control of much of the Barren Ogaden region of Ethiopia after a summer war between their two client states that the Soviets tried to prevent. Sources here agree that the Somalis expelled the Soviets perhaps in part to show other potential arms suppliers that Somalia wants nothing further to do with Moscow.

Reportedly encouraged in their move by the conservative Saudis, Somalia still cannot expect to receive arms from that country. The saudis are barred by the terms of their agreement with Washington from transferring any U.S.-made weapons to Somalia.

The Somalis may be entering a difficult time, sources here suggest. They have extended their supply lines across hundreds of miles of primitive desert, making themselves especially vulnerable to counterattack by the Ethiopians.

The Ethiopians, however, are in turmoil. There are deadly internal struggles for power within the leadership. Eritrean guerrillas continue to press in the northwest, and the Ethiopina military is in the throes of converting its equipment and tactics from years of American aid to Soviet machines and strategy.

Sources suggest here, however that should Ethiopia survive its present trials and emerge in reasonably sound condition in the next year or so, the Somalis' position may undergo rapid transformation from apparent winner to endangered combatant.

Meanwhile, the Soviets must seek new naval and air bases to replace those in Somalia from which they could reconnoiter both the Red Sea and Gulf of Aden, as well as the westport Indian Ocean. Their facility at the port of Berbera in Somalia was a partial answer to the American naval buildup at the new U.S. base on the British Island of Diego Garcia in the Indian Ocean.