Angola charged today that South African armored forces and jet fighters have penetrated deep inside the country in an action President Eduardo dos Santos called "so grave that it could provoke a war of unforeseeable consequences."

Dos Santos hinted in a telegram to U.N. Secretary General Kurt Waldheim that Angola may call on the estimated 20,000 Cuban troops in the country to help fight South Africans. Such a move could make the volatile southern African crisis a theater of East-West conflict and could cause a sharp deterioration of U.S. relations with black Africa.

The Defense Ministry in a communique published in the Jornal do Angola newspaper said today that two South African motorized columns using 32 tanks, 82 armored vehicles and their supports advanced yesterday toward Xangongo and Cahama, more than 100 miles by road from the border with Namibia. The previous day, the communique said, eight South African jets bombed Cahama and Tchibemba, almost 200 miles from the border.

South African reconnaissance flights flew over a 300-mile-wide area inland from Porto Alexandre on the Atlantic Coast, the government said. The Defense Ministry said "fierce fighting" was taking place between Angolan and South African ground forces, but it gave no details and no information on casualties.

The government radio announced tonight that all military leave had been canceled and all troops away from their units were to report to their bases within 48 hours. The 14-member Executive Secretariat, the top level body of the ruling party, met in emergency session all day.

South Africa refused to confirm or deny the reports.

The South African defense force in Namibia claimed that 29 "armed insurgents" and four members of South African security forces had been killed in the Namibian operation zone during the last 24 hours, Reuter reported.

Military analysts in Johannesburg said the guerrillas had been "clobbered" in the last few months. South African defense headquarters reported to Reuter that about 1,000 guerrillas have been killed this year.

Pretoria has frequently sent its forces across the Angolan border from Namibia in the last year in what it called "hot pursuit" of guerrillas of the South-West Africa People's Organization (SWAPO), which is fighting for independence for Namibia, controlled by South Africa in defiance of the United Nations.

In late July, Angola charged that South Africa had launched a major military operation, but South African Defense Minister Magnus Malan denied any large-scale operations in Angola. South Africa has repeatedly reserved the right to pursue SWAPO guerrillas across the Angolan border.

It was impossible to obtain independent confirmation of the Angolan report. All flights to southern parts of the country have been cut off. The area is about 750 miles south of Luanda, capital of this southern African country that is twice the size of Texas. President dos Santos' message to Waldheim caused serious concern among Western diplomats because it represented a public statement by the country's highest official of a warning previously issued to the diplomatic community by the Foreign Ministry earlier this month.

The Angolan leader said his country "may see itself forced to call upon Article 51 of the United Nations Charter for the defense of its sovereignty and territorial integrity."

The article provides for a country to call upon troops of a friendly nation to help defend its sovereignty.

Dos Santos' message said the South African troops along the Angolan-Namibian border were supported by "mercenaries and puppets," The Associated Press reported. This is believed to be a reference to the forces of Jonas Savimbi, the pro-Western leader of the National Union for the Total Independence of Angola (UNITA).

It said the "objective" of the attackers was "occupation of part of the sovereign territory of Angola."

Gilberto Morejon Bello, second secretary of the Cuban Embassy, said today, "For us it is a very dangerous situation."

Cuban and South African troops clashed previously in Angola during a civil war in 1975-76 following independence from Portuguese rule. The Cuban troops backed the new Marxist government and South African forces withdrew after driving to within 100 miles of the capital following a congressional ban on any U.S. support.

Asked about the fighting in southern Angola, which has escalated sharply in the last month, African diplomats said tonight that it "was the fault of the United States" because of the Reagan administration's policy of encouraging better relations with South Africa.

Angola has admitted that South Africa controls the airspace over the southern part of the country.

Yesterday the daily Angolan airlines flight form Luanda to Lubango, the major city in the south, turned back 15 minutes after takeoff under orders from civil aviation authorities.

An airline official said there were "operational problems" and denied "South African interference."

Today's flight never took off and passengers were told that "enemy aircraft are in Angolan airspace."

The military said in an earlier weekend communique that 10 South African Air Force jets violated Angolan airspace Friday "with the objective of preventing any supplies of emergency foodstuffs for the population of Cunene Province and, also, of preventing air traffic between Luanda, Lubango and Ondjiva."

That report said South African planes bombed a bus, killing 19 civilians, and attacked military and civilian convoys killing 16 others.