Leaders of the two guerrilla armies fighting the present Rhodesian government have reportedly agreed to unify their operations, but the report raised skepticism here.

Addis Ababa Radio said tonight that Robert Mugabe, who is based in Mozambique and Joshua Nkomo whose headquarters are here in Zambia, agreed to form a joint operational military command as well as a defense council and a political coordinating committee.

The also agreed to adopt a common constitution at a later time, it said.

The reported accord came after three days of intensive talks in the Ethiopian capital between the two nationalist leaders. They have been under enormous pressure from their African backers, as well as the Soviet Union and Cuba, to unite both their military and political organizations.

Nkomo and Mugabe are already co-leaders of the Patriotic Front, the guerrilla umbrella structure that is a "front" in name more than in reality and is in serious danger of splitting.

The Front already has a joint political coordinating committee and a defense council, but they seldom meet and have no real authority. It previously also had a joint military command but that no longer functions following bloody infighting between the two factions.

In addition, Mugabe's Zimbabwe African National Union (ZANU) and Nkomo's Zimbabwe African Peoples Union (ZAPU), sporadically have been discussing during the last year a constitution for the country.They have not reached an accord.

The radio report gave no indication that the two sides had made any real progress on the constitution, particularly on setting up a unified political party.

Some of the skepticism here about any real agreement was also based on the fact that Nkomo left Addis Ababa several days ago for Lagos, Nigeria, and was not present when Mugabe apparently announced the agreement at a press conference.

Had unity really been reached, the two leaders would almost certainly have announced it jointly.

Efforts to unite the two guerrilla factions have taken on more urgency since the April elections in Rhodesia in which 64 percent of the African population voted for a new black-led government under Bishop Abel Muzorewa. The new government will allow the white minority to retain a disproportionate amount of power. It is scheduled to take power by early June.

In addition, the victory of the British Conservative Party in the elections May 3 raised considerable concern among the Front's African supporters that the British may now recognize the new Rhodesian government.

The five African frontline states of Tanzania, Zambia, Mozambique, Angola and Botswana, the guerrillas' key backers, are also known to be extremely worried about the growing prospects of a blody power struggle between Nkomo and Mugabe that could persude some moderate African states to abandon the Patriotic Front and give their backing to the new Muzorewa government in Salisbury.