More than half the 450 deaths caused by South Africa's five-day incursion into southern Angola this week were Angolan government troops, South African officials said.

Many of those were killed when a garrison of Angolan soldiers at the tiny village of Xangongo, about 60 miles north of the border with Namibia, attacked South African forces on their way to assault guerrilla bases of the South-West Africa People's Organization (SWAPO), officials said.

If the South African version is accurate, it marks a significant development in South African military hostilities with its neighboring states. It would be the first time that government troops of a neighboring country stood their ground in a deliberate and massive way to fight a pitched battle with South African troops. Most of the clashes in the Angolan civil war in 1975 were between South African and Cuban soldiers.

In addition to the resistance of the Xangongo garrison, mixed Angolan and SWAPO troops on at least two occasions attacked the South Africans who had occupied the town, South African officials said. At the town of Ngiva, about 30 miles south of Xangongo, a mixed force also attacked the South Africans, officials here said.

Although this resistance was fairly easily routed by the South Africans, it was not without cost. Ten South African soldiers died in the week's operations, bringing the total number of South African deaths in the war this year to 51. More than 1,000 SWAPO insurgents have been killed, according to South African figures.

The South Africans gave their official explanation of the fighting this week in Angola to a pool of four foreign correspondents and a number of local reporters who were flown to Xangongo yesterday. After a week of silence on details of the incursion, the South Africans were eager to disprove Angolan claims they had made a full-scale invasion of that country.

In the U.N. Security Council, France sharply condemned South Africa's latest incursion into Angola and called for the immediate withdrawal of the invading force, Reuter reported.

"My government condemns in the strongest possible way the unprovoked and unjustified invasion of Angola by South Africa," Ambassador Jacques Leprette of France told the Security Council as it continued debate on Angola's complaint of aggression.

Reuter also reported that Angolan officials escorted the ambassadors of Britain, France and West Germany to the southern front for a firsthand look at the scene of the fighting.

Britain, West Germany and France all have condemned the latest South African Army attack against Angola. All three countries are members of the so-called Western contact group seeking a settlement in Namibia.

In their briefings to reporters here, the South Africans would not disclose how many troops they used in the operations, saying only that the figure was about a tenth of the 45,000 claimed by Angola. Mirage jets, helicopters and low-flying bombers were used as support for ground troops. The South Africans began withdrawing yesterday.

The journalists only saw the town of Xangongo, which is on the main north-south highway in Angola. It is not known if South African troops went farther north or if there were air strikes farther north.

The South Africans presented their activity as a continuation of their attempts to wipe out all SWAPO bases near the Namibian border. They said their extensive air and ground campaign against SWAPO camps in June 1980, which was code named Smokeshell, had severely crippled SWAPO in that area.

But since that operation it had been "difficult to get to SWAPO," according to Brig. Gen. Rudolf Badenhorst, commander of the South African troops in the northern part of Namibia. The Angolan forces had been "offering greater assistance to SWAPO in terms of base facilities under the umbrellas of their well-developed antiaircraft system and early warning equipment," Badenhorst said.

"This resulted in a situation where SWAPO could operate with relative safety from base areas close to the Namibian border," he said. "SWAPO exploited this situation to the point where it became dangerous and difficult for us to employ unconventional forces without a large degree of risk."

The South Africans said that their main aim in "Operation Protea," begun last Monday, was to destroy the Angolans' antiaircraft and radar systems at Xangongo that SWAPO was also using as a logistical center.

They said they accomplished this, and in addition, captured 200 tons of equipment and "a few" prisoners.

The South Africans said they dropped leaflets in Portuguese bearing pictures of the Angolan flag that warned Angolan forces not to interfere with the South Africans whose only quarrel was with SWAPO.

"Operation Protea went according to plan until FAPLA, the Angolan forces contrary to all warnings, interfered at a very early stage in Xangongo," Badenhorst said. "From the outset it was clear that FAPLA was not going to allow our forces to penetrate their protection to reach the SWAPO bases."

"So low-intensity follow-up operations resulted in casualties on our side inflicted by FAPLA elements interfering with our efforts.

"We were attacked before we reached the SWAPO base areas," he added.

The Angolans "must know that we are determined to destroy SWAPO. If they prefer to stand in our way they must be prepared to face the consequences," Badenhorst said. Sixty percent of those killed were Angolan forces, he said.