The Organization of African Unity summit today all but officially endorsed the Patriotic Front as the sole representative of African nationalists trying to free Rhodesia from white minority rule.

The ambiguous resolution adopted by the ideologically split conference, however, did not specifically withdraw the 49-nation organization's recognition from the Patriotic Front's purely civilian rivals. Bishop Abel Muzorewa and the Rev. Ndabaningi Sithole.

The resolution avoided the words "endorsement" or "recognition" in asking "all Zimbabweans" - as black Rhodesians call themselves - devoted to the struggle for the liberation of the Patriotic Front."

Joshua Nkomo and Robert Mugabe, leaders of the Patriotic Front which links the two rival guerrilla forces in an uneasy coalition, both spoke of the OAU's outright "recognition" of the Front.

So, too, did a Sithole spokesman who insisted "we don't eccept the decision at all" and warned that the resolution" nor makes it impossible for Zimbabwe to unite."

Significantly, both Mugabe and Nkomo, who less than a week ago poured scorn on their rivals, appeared to reflect the summitt's desire for nationalist unity by stating that the "door is open - to all comers" - albeit on their terms.

The Zimbabwe nationalist resolution was the most far-reaching decision taken at the four-day OAU summit otherwise marked by unprecedented attempts to avoid controversial issues and bickering.

Moderates, resurgent after a long dormant period, claimed victory of a sort in forcing approval of a resolution they claimed condemned Soviet and Cuban interference on the continent.

Despite the presence of 23 heads of state, little else was accomplished as the meeting in effect shelved immediate action on the many border quarrels around the continent by referring them to commissions.

Even the Zimbabwe resolution may disappoint the Patriotic Front, which had sought unequivocal OAU backing.

The resolution urged member states "to refrain from acts of supporting individuals thus running the risk of creating more than one army for the liberation and defense of an independent Zimbabwe."

Observers noted that neither Muzorewa and Sithole - both of whom command considerable support among blacks with Rhodesia - entertain serious pretensions about raising an army to challenge the Patriotic Front froces. Moreover, observers are not convinced that Front forces really constitute a single army.

Technically, the resolution did not prevent African countries from aiding Muzorewa and Sithole, noth of whom could claim they are heads of organizations.

Furthermore, relatively little of the money funnelled into the Zimbabwe nationalist organizations has been disbursed through the OAU, African nations and the Soviet Union, the guerrillas' main arms supplier, prefer direct dealings.

A Patriotic Front spokesman claimed the summit decision meant that now "the British no longer have the excuse that there's no single group they can hand over power to."

Britain still juridically responsible for its former colony of Southern Rhodesia which declared its independence in 1965, it trying with U.S. help to work out a peaceful transfer of power by sometime next year.

[The Anglo-American negotiating team trying to work out a political solution in Rhodesia arrived in Lusaka, Zambia, Tuesday night for discussions with Black nationlist leaders. The British negotiator, John Graham, said he hopes to reach a settlement eventually but "not in this round."]

The summit also:

Again shelved the problem of the Western Sahara where Algerian backed Polisario guerrillas are fighting Morocco and Mauriania, which annexed the former Spanish territory. A special meeting is scheduled to discuss the Sahara in mid-October.

Appointed two separte committees to study border disputes pitting Libya and Chad and Ethiopia and Sudan.

Adopted a Senegalese motion asking members to refrain from resorting to "foreign intervention" and from allowing their territory to be used as a "base of aggression" against another African country. This was meant by the sponsors to refer to non-African, especially Cuban and Soviet, operations in African.