The controversy over U.S. charges about a Soviet combat brigade in Cuba has obscured an important aspect of Cuba's role in international affairs: Fidel Castro's own 20 years of military diplomacy in the service of radical revolutionary movements around the world.

Because Castro's overseas activities usually have dovetailed with Soviet policy and profited from Russian financial and material support, there has been a tendency to regard his Cuban troops as communist-bloc "Gurkhas" hired out to Moscow in the service of Soviet expansionism.

In reality, though, the Cuban leader has not been a mere Soviet mercenary sending his soldiers across the globe at the Kremlin's dictate. Instead, Castro has chosen to involve himself in military conflicts beyond the confines of Cuba for reasons that transcend the revalries between Moscow and Washington.

Thus, whatever settlement of the current crisis finally is reached between the two superpowers, none of it is expected by U.S. experts to limit Castro's future military interventions in the civil wars and guerrilla revolutions of other countries.

Cuban military involvement in Africa, Latin American and the Middle East traces back almost to Castro's 1959 seizure of power.

As early as 1961, there was a handful of Cuban troops in Ghana giving training in guerrilla tactics; in 1963, Cuban tanks, other arms and more than 50 technicians arrived in Algeria to fight in the Moroccan border dispute; in 1965, about 250 Cuban military men went to Congo-Brazzaville to train a militia, and in 1973, about 200 Cubans went to South Yemen to provide both guerrilla and pilot training. Unconfirmed Israeli reports put Cubans in Syria that same year.

Over that same time period, small training groups of Cuban soldiers had worked in Guinea, Equitorial Guinea, Somalia, Zaire, Mozambique, Sierra Leone and Iraq.

Thus precedent existed for the 20,000 Cubans who went to Angola beginning in 1975 and the 16,000 who arrived a year later in Ethiopia.

The approach was slightly different in the Western Hemisphere, Castro's backyard, but the pace was no less hectic.

Training for guerrillas from Latin and Central American countries was begun in Cuba in the early 1960s; a Cuban-led guerilla group, headed by Ernesto (Che) Guevara, Castro's close friend, was discovered and destroyed in Bolivia in 1967 while similar Cuban-backed efforts were being quashed in Venezuela, Peru and Colombia.

Although the Cubans have been reported by U.S. intelligence sources as taking high casualties from their African ventures, exact figures are not known. But what ever they are, the dead and wounded have not dampened the island's support for Castro's deployments.

The overseas military adventures are accepted by the Cuban people, according to U.S. intelligence, "as an international responsibility to assist wars of liberation."

The Cuban job market is also overflowing and overseas military service, with special family and pay benefits, has become a means of advancement in the Cuban revolutionary society.

The Sandinista movement dedicated to the overthrow of Nicaragua's Somoza regime began in Cuba in 1962. Similar groups, opposed to regimes in El Salvador, Guatemala and Honduras, are represented in Cuba.

The Soviets provide direct and indirect financial aid to Cuba at a rate now pegged at $3 billion a year by U.S. intelligence. Shipments of military equipment also have been stepped up recently. The reason, according to a recent Defense Intelligence Agency briefing to a House subcommittee, was that in the past Cuba got older weapons but now "Cuba has been taking delivery of newer weapons systems comparable to those received by Moscow's other allied states. . . ."

Some American politicians and intelligence analysts look on this stepup of aid and the discovery of a Soviet combat brigade as signs of a new, direct Kremlin challenge to a weakened President Carter. But many Cuban experts in the United States see it only as an extension of what has gone on in the past, inside and outside Castro's island.

A 1977 Pentagon-financed study of Cuban military activities in Africa and the Middle East underscored the nature of the Havana-Moscow relationship.

The study rejected the assumption that Castro's dispatch of thousands of combat troops to aid the Marxist forces in Angola in 1975 was "a radical and dangerous departure in Cuban foreign policy . . . a calling-in of Cuban debts that led Cuban troops to fight as Moscow's all-purpose mercenaries in a war by proxy."

Instead, the sutdy said that "Though Angola was unique in some respects, in others it matches a pattern of Cuban military diplomacy established over the past decade and a half." In terms of Africa, that Cuban policy goes back at least to the 1961 Ghana mission.

A year or two later, a boatload of Cuban tanks -- obtained from Russia -- and military personnel arrived in Algeria to fight in the Moroccan border war. While it wasn't until the mid-1970s that Cuban troops began showing up by the thousands in countries like Angola and Ethiopia, their tracks have been discernible in many of Africa's lesser conflicts as advisers to the radical side in all the ensuing years.

These African involvements have been part of a larger pattern that has seen the Castro regime, throughout its years in power, identify openly with what it regards as Third World "wars of liberation" against imperialism and offer military aid to "progressive" regimes and revolutionary movements.

At different times, the main thrust of this aid has been directed at different areas -- Latin America in the 1960s, Africa and secondarily the Middle East in the 1970s and, in the upcoming years, possibly back toward Latin America, where increasing instability within Central America and the Caribbean could present Castro with new targets of opportunity for military assistance activities.

In most cases there has been a natural community of interest between these Cuban activities and Soviet policy. By cooperating militarily with the Soviets, Castro unquestionably has been able to make partial repayment to Moscow for the massive financial and economic assistance that enables him to maintain Cuba as an independent communist bastion 90 miles from the shores of the United States. Soviet subsidies often pay for troop and weapons transportation and Soviet equipment is provided Cuban forces overseas.

Although Castro regards the Soviet Union as Cuba's natural ally, he has always been assertive of Cuba's right to chart its own course in foreign affairs.

Throughout Castro's years in power, the dominant, unchanging thread in this course has been the line enunciated by his most famous collaborator, the late Guevara, who said: "The duty of every revolutionary is to make revolutions."

In short, Cuba has been willing to involve itself in foreign military adventures, not solely because it's been told to do so by the Soviets, but because Castro and his closest associates believe deeply that it is their duty.

In some instances, this Cuban belief blends easily with Soviet aspirations. That was the case in Angola where both Havana and Moscow emerged as natural allies of the Marxists contending for power in that country's civil war. But, as the Pentagon study notes, each took part for its own distinct reasons. The study said:

"Cuba had ample incentives of its own to send its troops to Angola, apart from any reasons the Soviets may have had, and independent of any Kremlin orders to do so. This is not to say that Cuba's behavior did not serve Soviet interests, but only to observe that Soviet behavior equally served Cuban interests -- the two sets converged."

There have been instances when Soviet and Cuban attitudes about foreign military aid haven't come together so neatly.

The most recent striking example has been in Ethiopia, where Cuba, at Moscow's urging, enthusiastically committed massive forces to help the Ethiopians repel an invasion from neighboring Somalia. But when the Soviets and Ethiopians then asked for Cuban aid in quelling the secessionist movement in the Ethiopian province of Eritrea, the Cubans balked on the grounds that they considered the Eritrean rebels' cause as a possible legitimate struggle for independence.

An even deeper schism occurred in the 1960s when Havana turned itself into a training center, refuge and source of arms for guerrilla movements trying to overthrow the governments of such Latin American countries as Venezuela, Colombia, Peru and Guatemala. In that period, Castro even tried unsuccessfully to promote the Latin American Solidarity Organization (known as OLAS after its Spanish initials) as a mechanism for fostering violent revolution throughout Latin America.

Such tactics ran directly counter to Soviet policy, which emphasized trying to win power in Latin America through orthodox, Moscow-line communist parties operating within the established political processes. In this, the Soviets were influenced partly by the desire to make some detente tradeoffs with the United States and partly by fear that Castro was trying to use the guerrilla movements to make himself the ultimate arbiter of communism within the hemisphere.

These differences put severe strains on the Soviet-Cuban relationship. It wasn't until the end of the decade when most of the guerrilla movements -- including Guevara's abortive foray into Bolivia -- had failed and Castro was encountering severe domestic economic difficulties that Moscow was able to exert sufficient leverage to cool off Havana's support of Latin guerrilla forces.