Over the dozen years since Rhodesia declared its unilateral independence from Britain, there have been innumerable negotiations to bring about black majority rule by peaceful means.

Talks on the latest plan, known as Prime Minister Ian Smith's "internal solution," got under way in earnest in Salisbury yesterday with reports of some progress. The main question is: what's new and different about these negotiation?

Some of the difference lies in the black participants, who represent only part of the myraid of black nationalist organizations that sound like alphabet soup to outsiders - ZAPU. ZANU. ZIPA. SUPO. The "Z" common to them stems from the African name for an independent Rhodesia, Zimbabwe.

The real significance of the variety of organizations is that some are fighting and others are talking in efforts to gain power. The history of independence wars in general has been that those with the guns are the ones that get the power.

That is the key problem for Smith's "internal solution" - he is negotiating with three moderate groups, none having troops, operating inside the country. The two groups doing the fighting are not involved.

Any agreement excluding the fighting groups could lead to civil war between rival factions in the 6.5 million black population, which could cause most of the 270,000 whites to flee. Foreign involvement, with the Soviet Union and Cuba waiting in the wings like in Angola.

Thus, a key element in Smith's negotiating plan is to maintain much of the white-controlled security forces. Another problem is how to transfer power from a white to a black government.

These problems were central to the failure of the first major American effort to end the Rhodesian crisis - Secretary of State Henry Kissinger's shuttle diplomacy last year. That failure led to a new effort by Britain and the new Carter administration, called the Anglo-American plan which, although not rejected, appears to be falling by the wayside.

The Anglo-American plan tries to avoid the transition problems by giving control to neither side. The Smith government would turn over power to an interim British administration, backed by an international peacekeeping force under United Nations control.

A new constitution providing for majority rule would be drawn up under British supervision as opposedto Smith dealing directly with the nationalists which he obviously prefers.

Smith's biggest objection to the Anglo-American plan is in the area of security. The black nationalist forces outside the country now fighting the government are to be trained by the U.N. forces to form thr bulk of the new army of Zimbabwe. It is left open for some personnel, or even units of the white-led Rhodesian military to join in this force.

No side has rejected the plan outright but support for it has waned considerably in the wake of what would appear to be Smith's counteroffensive - the internal solution.

Smith's strategy appears to be to take advantage of his oppenents divisions both among black Rhodesians and African nations supporting them.

Smith's opposition includes:

The two external groups. They are the Zimbabwe African People's Union (ZAPU), based in Zambia, supported by the Soviet Union and led by Joshua Nkomo: and the Zimbabwe African National Union (AZNU), headquartered in Mozambique, backed mainly by China and headed by Robert Mugabe.

The two groups, althouth not always seeing eye to eye, have formed what is called the Patriotic Front to carry on the fighting under what is theoretically a joint military effort called the Zimbabwe Independent People's Army (ZIPA). There have been indications that Smith has been trying so far without success to split the more moderate Nkomo from Mugabe, a professed Marxist, and bring Nkomo into the internal talks.

The three groups operating inside Rhodesia and now talking to Smith. They are the United African National Council (UANC), led by Bishop Abel Muzorewa: the African National Congress (ANC), headed by the Rev. Ndabaningi Sithole; and the Zimbabwe United People's Organization (ZIPO), of Chief Jeremiah Chirau, who is generally regarded as being the most willing to reach a settlement with Smith.

The "front-line" nations. These are five southern African nations - Tanzania, Zambia, Botswana, Mozambique and Angola - that are trying to apply international pressure to bring about a settlement. Of late, divisions have developed in their ranks too, notably between Zambia and Tanzania.

The latest talks are the direst result of an announcement by Smith last month committing himself for the first time to "the principle of majority ruled based on adult suffrage."

This has generally been taken to mean that after years of agonizing. Smith has come out in favor of one-man, one-vote, although he did not use the specific terminology.

As recently as last year Smith had said: "I do not believe in black majority rule - not in a thousand years."

Six months after that statement, however, 1,000 years had shrunk to two as Smith, at Kissinger's urging, reluctantly agreed to a British plan aimed at achieving majority rule in 1978, although presumably involving a limited franchise.

Smith's metamorphosis follwed the 1974 Portuguese revolution which led to black governments in Mozambique and Angola, the ongoing guerilla war causing an exodus of 1,000 whites a month, and tacit South African pressure.

The problem for the Africans dealing with Smith is whether they can believe him even if they reach agreement, since he has managed to shift positions on numerous occasions during his 12 years in power.

As Richard M. Moose, Jr., assistant secretary of state for African affairs, said recently: "In dealing with Smith, one can never be too careful."