The South African defense minister has warned that the Angolan government's two-month-old offensive against the rebel movement in southern Angola threatened this country's regional security interests. He said his Army would "react" against the threat.

Gen. Magnus Malan, in an interview published today in the Afrikaans-language newspaper Beeld, said he would not rule out "military intervention" against the Angolans, who are equipped with advanced Soviet weaponry and supported by Cuban and Soviet military advisers. Angolan forces are fighting Jonas Savimbi's National Union for the Total Independence of Angola.

A team of senior South African diplomats left for Washington this morning. Analysts here say the team must be seeking either American diplomatic intervention with the Soviet Union to blunt the Angolan offensive or American support for the rebels.

South African officials, citing Savimbi's weekend statements from his headquarters in Jamba, said the Soviets have taken a much more active role in the current offensive than in previous assaults against the guerrillas and said his remarks underscored their own concerns about the possibility of a wider conflict in Angola.

Cuban troops in southern Angola are deployed in defensive positions and have made a point of avoiding direct engagements with either South African troops or rebel forces, according to diplomatic sources. About 25,000 Cuban troops are stationed in Angola.

Malan's statement, following his admission last week that South Africa provides aid to Savimbi, reflects the rebel leader's continued importance to Pretoria's military planners.

The occupation of large portions of southern Angola by Savimbi's forces has helped prevent rebels of the South-West African People's Organization (SWAPO) from using the territory to stage attacks on the South African-controlled territory of Namibia, which borders Angola. It also has helped tie down, by South African estimates, 4,000 to 5,000 combat-trained SWAPO guerrillas who have been helping defend Angolan bridges and other sites against UNITA attacks.

If the UNITA threat were eliminated or reduced, the reasoning goes, these insurgents would turn their attention to northern Namibia.

South Africa also views UNITA as a critical element in its overall geopolitical strategy. "They see Angola as the key to the region," said Michael Hough, director of the Institute for Strategic Studies at the University of Pretoria. "UNITA is their counterinfluence to Soviet involvement. If it falls, the entire region could be radicalized. Angola would provide the Soviets with a reliable center from which to operate."

South Africa already has made two air strikes against the Angolan forces besieging Savimbi's insurgents, according to the Angolan government. Pretoria must now decide whether to send in ground troops.

To do so would be a great risk, western analysts say, because of Angola's improved air-strike capability. The lengthening of the government airstrip at Menongue in southern Angola has put UNITA's forces within range of Soviet Sukhoi bombers and MiG fighters. The South African military has not indicated whether Soviet or Cuban pilots are involved in the current drive.

At the same time, a vastly improved Soviet-manufactured air defense system would make it difficult for South Africa's efficient but aging Air Force to maintain the air superiority it has previously enjoyed.

Faced with this, analysts say, the South Africans have sent their mission to Washington to enlist U.S. support.