JAMBA,Free Angola-Why, having liquidated its East European empire, does the Soviet Union continue to poor billions in scarce resources into unreformed, non-European Marxist governments that rely on old thinking and old tactics in their effort to maintain power?

If the Soviet government is no longer committed to the idea of an international class war destined to end with the triumph of Marxism, why in the world should it invest such disproportionate amounts of money and materiel in such unpromising places as Afghanistan, Ethiopia, Mozambique, Angola and Cambodia -- places where repressive one-party governments manage hopelessly inefficient economies under continuing siege by insurgent armies?

Why shouldn't the Soviets accept for these countries the same sort of settlement they accepted in Nicaragua and in Namibia: free elections under international supervision?

It makes no sense for a Soviet government willing to submit its own majority to the test of opposition and election to squander resources on such artifacts of a previous era as the one-party dictatorships of Afghanistan's Najibullah or Angola's Eduardo dos Santos.

Consider Angola. No government has any real interest in protecting the sinecure of Angola's ruling Marxist regime, the MPLA. It is, in any case, extremely unlikely that any amount of money or war materiel can finally maintain this government in power.

Former ''colonials'' call the sorry state of affairs in Angola the result of ''Africanization.'' The MPLA blames civil war. Neither is correct.

It is not fair to describe as ''Africanization'' the process of continuing deterioration and decay to which the cities and economy of Angola have succumbed in the 15 years since Portugal's abrupt departure from that country. Angola was overcome less by ''Africanization'' than by the very European disease of Marxism, with its policies of nationalization, central planning and control, its reliance on coercion and its elimination of the market and associated incentives.

It is also not true, as MPLA apologists pretend, that civil war has caused the decay of Angola's economy and the disorganization of its society. The reverse is more nearly the case. Luanda is not a city under military attack. It is a city ravaged by incompetence, corruption and waste.

Even with 60,000 troops and additional thousands of Soviet, Czech, North Korean and East German advisers, and even with military assistance amounting to billions of dollars annually, the MPLA has been unable to defeat the challenge of Jonas Savimbi and his UNITA resistance. It is true that Savimbi's forces have also enjoyed assistance from various non-Communist governments in Africa, the Middle East, Europe and Asia -- including the United States and South Africa -- but UNITA's aid has never approached the billions provided by the Soviets and the ''world socialist system.''

The MPLA is simply outmatched.

UNITA has survived, even against the recent offensive at Mavinga, because its forces are well organized, highly motivated and well led.

Of Jonas Savimbi himself, an African head of state said to me, ''He is a classical hero who lives with his army in the bush and shares its hardships, who leads his men into battle and shares their risks. He is also the only African who has understood how to sustain a guerrilla war.''

I do not know if Savimbi is the only contemporary African leader who possesses the skills required to sustain such combat. But it is clear that he has managed to inspire the kind of loyalty the MPLA has found it necessary to coerce and that he has had the imagination and political skill to win needed support from a wide variety of other governments.

Savimbi learned from the master of guerrilla war, Mao Tse-tung, how to strike where it hurts most and how to organize his own forces for a long-term struggle. He knows how to build a revolutionary army that provides food and clothing, schools and hospitals to its soldiers and their families.

He is also sophisticated enough to understand the irony in the fact that he practices socialism in Jamba while advocating a market economy for Angola. ''We are an army at war,'' he shrugs, ''not a normal society.''

His overriding goal now is to end the war and become that normal society. Savimbi wants for Angola what Namibia achieved: free elections under United Nations supervision.

With Clausewitz, he understands that the principal target must be the will of his adversary. In fact, he thought he had already effected it.

''One might have thought that the MPLA's defeat at Mavinga would leave them ready to negotiate,'' he observed to me two weeks ago. ''The fact that we seek negotiations in the wake of victory should persuade them that we seek peace and want to rebuild the country.

''Africa needs peace and democratic elections just as much as Europe does,'' Savimbi asserts. ''The Angolan people have waited for 15 years for democratic elections. It is not reasonable that they should have to wait longer.''

What Angolans want is probably what Afghans, Cambodians, Mozambicans, Cubans and Vietnamese want as well.

Why should the Soviet Union not cooperate in giving these unfortunate client states the same privileges it now accepts for Eastern Europe?