Zimbabwe political merger strengthens leader's hand. Mugabe gains long-time goal of one party, and opportunity to reshape government

The unity pact signed between Prime Minister Robert Mugabe's ruling party and Joshua Nkomo's opposition party creates an opportune time for Zimbabwe's ruler to make some key political changes. Mr. Mugabe is expected to bring some opposition members into his Cabinet and at the same time drop a couple of unwanted members of his own party.

The government hopes that once Mr. Nkomo and two or three of his colleagues are given Cabinet posts, dissident activity by antigovernment bandits in Nkomo's stronghold, the western province of Matabeleland, will wind down. But some political analysts here say Nkomo has little or no influence on the extremists who claim to back his party but whom he repeatedly disowns.

Some opposition party activists describe the unity agreement as a pact between the leaders that has left grass-roots followers, on both sides, out in the cold. They say Nkomo is regarded by many in Matabeleland, where the Ndebele tribe is dominant, as a spent force. They say unity will only work if the government steps up investment in the disaffected province and agrees to decentralize some ministries and appoint Ndebele supporters of the opposition to senior posts in the region.

In the 12 months preceding Tuesday's signing of the pact, two years of off-on unity talks had completely broken down and, in October, the government closed opposition party offices. At that time, Nkomo criticized the steps taken by the ruling party to establish a one-party state based on Marxist-Leninist principles.

Now, however, Nkomo has agreed to such a pact, under which the new post of president will be created and the country's sole party will be called Zimbabwe African National Union-Patriotic Front (ZANU-PF), the current name of the ruling party. Mugabe will be president and party leader. Nkomo, formerly leader of the now defunct Patriotic Front-Zimbabwe African People's Union (PF-ZAPU), is expected to be one of two party vice-presidents.

ZAPU and ZANU were linked in a loose coalition known as the Patriotic Front during the guerrilla war against white-ruled Rhodesia, which ended in the collapse of the white government and independence in 1980.

The most important aspect of the executive presidency could be the opportunity it creates for Mugabe to shuffle his Cabinet. In so doing, he must keep a delicate balance between the mutually suspicious tribal groupings, find places for at least three ZAPU ministers, and rid himself of some embarrassing senior ministers.

The two ministers thought most likely to be axed are the controversial - but still very powerful - transport minister, Herbert Ushewokunze, and Foreign Minister Witness Mangwende, who is widely considered inept.

Mr. Ushewokunze has been strongly criticized by the government for his administration of both Air Zimbabwe and the national railways. Mr. Mangwende, much disliked by Western diplomats, recently attacked the United States during a UN speech. His speech came at a time when State Department officials were working to resume aid to Zimbabwe that has been frozen since a spat between the two nations in July 1986.

Mugabe is reported to have said privately that he will get rid of ministers who have breached the party's leadership code regarding restrictions on personal investments and business and farm ownership. But analysts say this will be very difficult because at least half the Cabinet would have difficulty in meeting the regulations.