Three days after military strikes against alleged black guerrilla targets in three neighboring states, South African troops crossed into southern Angola, killed 53 government soldiers and wounded five others in an artillery and armored car attack, the Angolan Defense Ministry said today.

A statement, reported by the official government news agency ANGOP and monitored here, said South African ground forces launched the action last Thursday in support of antigovernment rebels 40 miles north of the border with the South African-controlled territory of Namibia.

The Angolan troops came under heavy artillery fire as they engaged in a "cleanup" operation against UNITA guerrillas 25 miles southwest of Xangongo in southern Cunene Province, according to the statement.

It also said South African military aircraft and armored columns violated Angolan territory in eight other operations detected between May 1 and May 19, one of them allegedly involving 600 troops. The statement followed repeated Angolan denunciations in recent months of an alleged South African military buildup on Namibia's border with Angola.

[In Pretoria, a South African Defense Force spokesman refused direct comment on the Angolan statement, Reuter reported. "We have nothing to add," the spokesman said.]

Angola condemned the alleged operations as part of a "systematic policy of destabilization" by South Africa's white-minority government against neighboring black-ruled states. That included the May 19 attacks against alleged black South African guerrilla facilities in or near the capitals of Botswana, Zambia and Zimbabwe, Angola said.

The statement said South Africa had singled out Angola as its principal target, engaging in "constant acts of sabotage" and increasing direct military action in support of UNITA. The rebels have been fighting since 1975 to topple the Soviet- and Cuban-backed Angolan government.

The Pretoria government maintains that its troops only cross into Angola in "hot pursuit" of black guerrillas fighting for Namibian independence.

UNITA said recently that Angola had been preparing a further offensive against its bush headquarters, but now was hesitating because of the supply of U.S. arms to the rebels. In January, President Reagan reportedly pledged rebel leader Jonas Savimbi $15 million in aid, including sophisticated ground-to-air missiles.