Political merger in Zimbabwe would consolidate leader's power. But some members of opposition fear they would be relegated to lesser status if their party joined ruling party

If Zimbabwean Prime Minister Robert Mugabe really has managed to secure a merger of his ruling ZANU-PF party with Joshua Nkomo's ZAPU, it will be a major personal triumph. Government officials and the government-controlled news media are maintaining a tight-lipped silence on the issue, but senior officials in the opposition party and Western diplomats say a breakthrough in the unity talks was achieved last week.

In terms of the draft agreement, a new party to be called ZANU -- dropping the ``patriotic front'' element from the name -- would replace Mr. Mugabe's ZANU-PF (Zimbabwe African National Union-Patriotic Front) and Mr. Nkomo's ZAPU (Zimbabwe African People's Union).

Mugabe would be president of the new party and Nkomo given the largely titular post of second vice-president which would rank him No. 3 in the new party hierarchy after Deputy Premier Simon Muzenda.

It is reported that agreement has also been reached on such contentious issues as the release of political detainees and the return of political exiles. The draft agreement is now with the two party leaders who are due to meet soon to finalize the deal.

Last minute snags are always possible, especially as some government ministers reportedly oppose the deal.

But Mugabe is anxious to push it through for two main reasons. First, he hopes that the merger will finally isolate the so-called dissident gangs operating against government security forces in the southwestern part of the country.

To date they have killed upwards of 300 people and are tying down large numbers of troops and police in the region.

Second, the agreement would mean that Mugabe will have taken a giant step toward establishing his long-cherished one-party state. The Constitution now prohibits those changes needed to effect a one-party state. But a voluntary agreement to establish a one-party state would allow the government to proceed without any constitutional obstacles.

A key issue will be the reaction of the 120,000-strong white community. Under the Constitution they have 20 reserved seats in the 100-seat Parliament. Mugabe is anxious to abolish this privilege pointing out that it is anachronistic to allow 20 percent of parliamentary to less than 2 percent of the population.

Mugabe could abolish the white seats if he can get 70 of the 100 members of Parliament to vote for such legislation after 1987, when the Constitutional clause protecting those 20 seats expires. With the merger of the two parties he would control 79 seats, so it would be possible to eliminate reserved white representation before the next elections due in 1990.

Meanwhile, Ian Smith, leader of the largest bloc of whites in Parliament -- his Conservative Alliance holds 15 of the 20 reserved seats -- has indicated a willingness to discuss the whole issue of minority representation rather than run the risk of seeing such representation abolished without any alternative being offered. Mr. Smith, who was prime minister of Rhodesia, as Zimbabwe was known before independence, said over the weekend that his party was already discussing representation with government mi nisters.

Even at this late stage, the merger could still go sour if the rank and file on either side, and especially in the ruling ZANU-PF, seek to block it. But this looks unlikely. When the terms are finally released, it is likely to become apparent that the merger is, in reality, a takeover, analysts here say.