Angolan rebels today freed two captured Soviet airmen in the first phase of a multinational prisoner exchange that is to culminate here Tuesday with the release of three Americans imprisoned by the Angolan government.

The complex Lusaka swap, which has been under negotiations on three continents for almost two years, also will include another Russian held by South Africa plus a number of Cuban, South African and Angolan prisoners. The exchange also includes several bodies. The prisoners and the dead are the result of South African invasions of southern Angola to fight Namibian guerrillas based there and a guerrilla war against Angola's pro-Soviet government.

One of the Russians freed today told an Associated Press reporter at the scene that he had been treated well. "I want to go home and improve my health and go to work," Mollaeb Kolya said.

Two of the American prisoners are mercenaries captured during the 1976 civil war in Angola, while the third is a civilian pilot, Geoffrey Tyler, 32, of Seabrook, Md., who crash-landed his airplane on a beach in southern Angola 21 months ago.

One of the mercenaries, Gustavo Grillo, 33, of Jersey City, N.J., has been serving a 30-year sentence since he was convicted by an Angolan tribunal in June 1976. The other, Gary Acker, 27, of Sacramento, Calif., was sentenced to 16 years.

The swap has been scheduled a number of times, only to fall through at the last minute. Sources who declined to be identified cautioned that even though the Angolan rebels have released the Soviet pilots to the Red Cross in Namibia (South-West Africa) to begin the complicated exchange, "at any stage any of the parties can call it off."

The exchange was negotiated by the International Committee of the Red Cross based in Geneva.

The United States is the only major nation that refuses to recognize the Marxist government of Angola. The Luanda government, in turn, has refused to have any dealings with guerrillas of the Union for the Total Independence of Angola (UNITA), who are led by Jonas Savimbi.

The two American mercenaries, who fought for the Zairian-based National Front for the Liberation of Angola, (FNLA) were captured in February 1976 in northern Angola and were among 13 mercenaries convicted in a show trial. Three British mercenaries and one American, Daniel Gearhart, of Kensington, Md., were executed in July 1976 despite clemency pleas from president Gerald Ford and British prime minister James Callaghan.

The mercenaries were part of a clandestine operation by the U.S. Central Intelligence Agency to bolster the FNLA and UNITA guerrillas in an unsuccessful attempt to prevent the Marxist Popular Movement for the Liberation of Angola (MPLA) from gaining power in a civil war. The strife followed a 10-year guerrilla war leading to Portugal's 1975 withdrawal from colonial rule in the oil-rich West African country that is twice the size of Texas.

The CIA spent more than $30 million on the operation, which was cut off by Congress after South African troops invaded Angola in support of Savimbi's forces. The MPLA won the civil war with the support of Soviet military equipment and advisers and 15,000 to 20,000 Cuban troops who have remained in the country and have become a bone of contention in negotiations for independence for neighboring South African-controlled Namibia.

The release of the two Russians signaled the beginning of the exchange. Kolya, a 40-year old pilot, and Ivan Chernietsky, a 48-year-old mechanic, were captured when their Soviet troop-carrying plane was shot down by a surface-to-air missile over southern Angolan by UNITA guerrillas.

Savimbi today turned the Russians over to the South African Red Cross in southern Angola near the Namibian border, and they were then taken to Namibia and turned over to the ICRC to await the next phase of the transfer in Lusaka.

In Seabrook, Md., Tyler's mother said in a telephone interview, "I'm just on pins and needles waiting." Marjorie Tyler said she had received about 10 letters from her son and had been allowed to send him care packages.

The Associated Press reported the following:

Savimbi said in an interview in his thatch-roofed hut that serves as his headquarters somewhere in the southern Angolan bush, "We agreed to release the two Russians because the American administration of President Reagan has asked us insistently since last November.

"They contacted me directly because they wanted to get their citizens out of Angolan jails."

Savimbi handed over the two Soviets to Dr. Piet Smit, president of the South African Red Cross, under a banner saying, "Let's stop the Soviet mad dream," a reference to the spread of East Bloc influence in mineral-rich southern Africa.

Red Cross officials allowed an AP reporter to accompany them into the rebel-held area and to meet the freed Soviet airmen.

Kolya, of Moscow, said he "came here to help improve the transport system. We were offered a contract to work for one year or two years. We were flying cargo around in boxes, and passengers. We never saw what was in the boxes."

Married and the father of two children, Kolya spoke in Russian, which was translated into English by a Red Cross interpreter.

"We could wash. We had clothes. We were well-treated," he said of his captivity.

Chernietsky, of Kiev, said Savimbi's guerrillas told him Thursday that he was to be freed. His captors also informed him of the death of Soviet president Leonid Brezhnev, Chernietsky said.

Savimbi said he also has promised the Vatican he will free the Angolan Roman Catholic Archbishop of Lubango, Msgr. Alexandre do Nascimentos, who was abducted by UNITA fighters in mid-October.