AMERICANS tuning in the news in recent months could again view bombing of hospitals and civilians (in East Africa) or watch guerrillas being killed (in Rhodesia), as if the Vietnam War were being rerun. Between the Vietnam War and the heating up of African wars, however, the laws of war were updated.

At a four-year-long Geneva Conference on Humanitarian Law, attended by the United States and some 120 other nation, two protocols were adopted. As of December, these additions to the 1949 Geneva Conventions - new instruments of "Red Cross law" - are open for the signature of the United States and other nations.

How this first revision of humanitarian law in more than a generation was shaped by shifts in regional and international power alignments and by the continuing struggle between West-East blocs and more recent North-South divisions was evident in the key article of the first protocol of 1977. That article defines a new category of war: "Armed conflicts in which peoples are fighting against colonial domination and alien occupation and against racist regimes in the exercise of their right of self-determination."

This definition was promoted by the Third World - which had the largest bloc of votes at the conference - and its preoccupation with South Africa, Rhodesia and Israel. The new law presumably would compel these governments, confronted by "liberation movements," to invoke provisions indirectly recognizing the strength of these movements and conferring the status of prisoners of war on their fighters.

The United States and other western governments first opposed similar but more moderate wording, then caved in to the realities of voting strength and accepted the more flamboyant passage.

Nothing in international law, however, gives the World Court at The Hague or any other institution the right to say when such a war exists. That judgment is still left up to the fighting parties, and it takes a good deal of faith to believe that Rhodesia, South Africa or Israel would admit to being colonialist, racist or even an occupying power in the full legal sense. So the new law may never be invoked by any of these states. The Third World victory may be more semantic than real.

On the other hand, Third World states fought against significant extension of humanitarian law to internal wars. These states, having advocated the adoption of rules that would restrict the three countries they regard as pariahs, did not want new rules that might restrict, for instance, Iraq in dealing with the Kurds, Ethiopia with the Eritreans or Indonesia with the South Moluccans.

Even Britain was not too keen on some of the western proposals on internal wars; its eye was on its freedom of action in Northern Ireland. Yet Canada, and at a crucial moment the chief delegate of Pakistan, kept pushing for a new law. Eventually, 28 new rules were added to the one rule from 1949 (which until now has been the only piece of treaty law on internal war). Intervention Feared

THE SECOND protocol, like the first, does not authorize a neutral party to say when an internal war exists.In the past, Ethiopia and other states have contradicted reality by denying an internal war was in progress within their boundaries. Some Third World states, remembering the Nigerian civil war, fear intervention in what they regard as their internal affairs. Even if Third World governments sign and ratify the second protocol - and many are not likely to - considerable problems would remain in getting an established government to admit that a secessionist movement or other non-established force was powerful enough to have waged an internal war. The British have never admitted that in Northern Ireland.

Debate over the legal status of mercenaries, another sticking point, also reflected North-South ideological differences. Many Third World delegations regarded mercenaries as beyond the pale of humanitarian concern and not worthy of the protection of the laws of war.

The Soviet Union supported this position, apparently eager to score diplomatic points among the less-developed countries. Western states and Red Cross spokesmen strongly opposed these efforts, noting that for more than 100 years humanitarian law and the International Red Cross had tried to protect individuals without regard for the justness of the cause for which they fought. The United States and its allies recalled with concern the execution of American and European mercenaries recently in Angola. A compromise was negotiated under which mercenaries captured in international wars, while denied the label of prisoner of war, would be accorded such fundamental guarantees as protection against being tortured or murdered. Most of the same guarantees were written into the protocol on internal wars. Protecting Powers

WHILE NORTH-SOUTH conflicts dominated much of the conference, they were crosscut by East-West disputes, some procedural, but one of major substance.

Certain western states like Belgium strongly favored interjecting an automatic substitute for a "protecting power" in international war. A protecting power is a neutral state, appointed by one belligerent and consented to by the other, to promote humanitarian interests, as Switzerland and Sweden did in World War II. It has not always been possible to gain agreement on a protecting power. The United States wanted to appoint Egypt the protecting power in the Vietnam War, for example, but Hanoi never indicated its support.

But the Soviet Union objected strenuously, arguing that an automatic substitute not subject to ad hoc consent by one of the warring states would violate national sovereignty. Some western states such as France, which sided with the Soviet Union on similar issues arising out of United Nations peacekeeping in the Congo in the 1960s, were not enthusiastic about Belgium's position. When the United States did not press for adoption for automatic substitution, and when the International Committee of the Red Cross sided with the East Europeans, the proposal died.

In sum, the development of new rules for warfare proved no different in certain respects then the wrangling over a new law for the oceans or for a global economic order. Concerns about power, ideology and autonomy of national decision-making were strongly articulated.

Still, the process of "humanizing warfare" did advance a few notches. A number of humanitarian concerns were written into the law.

One victory consisted of holding ground. It had been feared that the spread of guerrilla activity and military technology since the 1949 Geneva Convention had eroded the principle that civilians are not permissible targets of attack. But the new protocols reaffirm the principle.

How effectively it can be applied in the future is another matter. Guerrillas (and some counterinsurgency forces) sometimes view civilians as politically useful objects for destruction. Insurgent forces may, for example, want to wipe out civilians to demonstrate that the government they seek to overthrow cannot control its own territory. Nonetheless, it is encouraging not only that civilians were excluded as permissible targets but that bona fide military targets were defined for the first time under general formulas.

Also prohibited for the first time were saturation bombing of cities, regardless of whether they contain military targets, and attacks designed to spread terror among civilians, such as the air raids on German and British cities during World War II.

Furthermore, indirect assaults on civilians are banned. These include warfare intended, or likely, to create "widespread damage to the natural environment" and attacks on dams, dikes, nuclear plants and other facilities whose disruption would inflict harm to civilian populations.

And for the first time in the long history of international law deliberate starvation of civilians was proscribed as a method of warfare. Presumably this would include sieges and blockades that deny vital foodstuffs to civilians as well as long-lasting crop defoliation.

Thus there is no longer ambiguity in international law about the repetition of some of the worst events of the Vietnam War, such as North Vietnamese attacks on civilians, American bombings, the Phoenix program of political murder and use of defoliants that cause long-term damage to agricultural lands.

As yet this legislation has had no noticeable impact on fighting in Ethiopia and Somalia, where combatants still attack civilians regularly, but the ink is barely dry on the 1977 Geneva Convention. Guerrilla Activity

COMBATANTS also are afforded additional protection under the new protocols. So long as guerrillas themselves adhere to the laws of war, for example, they must be considered prisoners of war when captured. POW status under the 1949 Geneva Convention required that combatants wear uniforms and carry their arms openly at all times. Guerrillas need no longer meet these conditions. However, they must distinguish themselves from the civilian population immediately before and during an attack. A terrorist who secretly plants a bomb in a market is, if captured, not to be accorded POW status.

The new protocols thereby take realistic account of the growth of guerrilla activity as a pattern of warfare and offer an inducement to the "irregular" soldier to observe the rules of war. Otherwise he is subject to prosecution under national laws on murder, treason, subversion and the like.

Humanitarian progress also is reflected in new rules that should facilitate the evacuation of battle wounded, thereby reducing mortality rates and quickening recovery from injuries. Medical flights over contested territory in which combat is under way are guaranteed neutrality. Except when flying over territory controlled by the enemy, medical aircraft need no longer file flight plans with the enemy to assure they will not be fired upon.

This political struggle over updated humanitarian law did produce advances, even if the vested interests of most states may keep them from taking any radical steps. Much remains to be done, but it is hard to imagine that the Carter administration, with its emphasis on human rights, could fail to sign these protocols on human rights in armed conflict.