The Post's editorial {Sept. 15} concluding that the United States should "do more" in providing humanitarian food aid to Angola reflects the only humane response to a growing crisis that will affect millions of innocent people, especially the women and children who are the primary victims of a famine.

However, the editorial gives a totally false argument about why Angola has been forced to ask for international relief. To contend that the Angolan government "chooses to expend very little of its available resources on its hungry citizens" ignores the very reason that famine is stalking this potentially wealthy land: that a war fueled largely by South African aggression -- and now, sadly, by American complicity -- is destroying the country's economic infrastructure.

South African troops first invaded Angola at the time of its independence from Portugal 12 years ago, and since then South Africa has maintained an active military presence in the country, both indirectly through its support of Jonas Savimbi's guerrilla group UNITA and directly with troops, bombing missions and terrorist incursions such as the 1985 attempt to blow up Angola's vital oil fields. The principal tactic of both South Africa and UNITA, as documented by international relief organizations and The Post's own reporters and publicly acknowledged by Mr. Savimbi, is to destroy the country's economy. One method of achieving that goal, again verified by objective sources, is to terrorize the rural population by planting land mines in the fields, which has made Angola the country with the largest per capita population of amputees in the world.

Angola does "choose" to spend resources on its citizens, as does any concerned government. And its progress until the war intensified in the areas of health, literacy and infant mortality was praised by UNICEF and other international agencies. But how much choice is left when an enemy, financed and supplied by such powerful allies as South Africa and the United States, specifically targets doctors, teachers, nurses and agricultural workers, not to mention the hungry citizens in their fields? How much choice remains when an enemy attacks railroads, highways and other transportation networks?

If there is anyone doing any "choosing," it is the Reagan administration, which has decided to help perpetuate South Africa's war in Angola by sending millions in aid, as well as Stinger missiles, to further the tactic of economic strangulation of Angola's innocent population.

JOSE LUIS DE MATOS AGOSTINHO Press Attache' Permanent Mission of the People's Republic of Angola to the United Nations New York