Aden brings Libya, Ethiopia together?

South Yemeni President Ali Nasser Muhammad has made it plain that the Aden summit of pro-Soviet leaders is to counter increased United States and Western military activity in the region.

But informed Arab sources report that it may have been a dispute between two of the three participating countries -- Libya and Ethiopia -- which finally brought about the present summit.

Libya's Colonel Qaddafi, these sources say, had long ago toned down his previous support for Eritrean secessionists in Ethiopia, out of solidarity with the radical regime in Addis Ababa. He was therefore disappointed that the Ethiopians did not return the favor with more enthusiastic support in African forums for his present stand in Chad.

The colonel and his allies in Syria and the Palestine Liberation Organization (PLO) have also been worried over recent months by increasing signs of a rapprochement between Ethiopia and Sudan, which is a pariah in the hard-line Arab camp for its renewal of relations with the Egypt of President Sadat.

The Arab hard-liners were thus keen to bring Ethiopia back into line and the Soviets were presumably also eager to see their allies near the Horn of Africa acting in tandem rather than at cross-purposes. In the end, the sources say, it was PLO radicals who urged the three heads of state get together to solve their differences, and the results, if regional coordination between them really is stepped up, could be better for the hard-liners than even they had hoped.

Arab hard-liners stress that the primary importance of the meeting in the South Yemen capital, Aden, will be for Africa, but it could also have far-reaching consequences for the Red Sea arena, and further east, for the whole of the Arabian peninsula.

Signs of a current upsurge of South Yemeni confidence in regional affairs include:

* The dispatch, during the Aden summit, of a South Yemeni envoy with a message from President Muhammad to his North Yemeni counterpart. Coordinaton between the two states has continued intermittently since the cessation of border skirmishes in 1979, and North Yemen has given signs of tilting in recent months even further away from the Saudis, who generally counterbalance radical South Yemeni influence in their affairs.

* The publicity given during the summit to a meeting between President Muhammad and a delegation from the Popular Front for the Liberation of Oman (PFLO). PFLO rebels battled the pro-Western Sultan in Oman with South Yemeni help between the late 1960s and the mid-1970s. Its reactivation in recent months could signal the end of a tacit cease-fire between the Sultan and Aden.

* Contacts between Aden and Ayatollah Khomeini's Iran continue, though Khomeini is loathed and shunned by all other Arabinan peninsula governments.