Preliminary peace talks this week marked an unprecedented step toward ending Angola's civil war, but the warring parties face a daunting task in securing an outcome that allows them all to save face.

Since the war began in 1975, the antagonists have been given to belligerent talk. It will not be easy for them to tone down their rhetoric if they feel that national honor is at stake.South Africa has justified its support of the Angolan rebel movement UNITA as necessary to thwart a communist onslaught in southern Africa. Angola's Marxist government, backed by 40,000 Cuban troops and about 1,000 Soviet advisers, has derided UNITA as a puppet of South Africa's "racist regime."

The two-day talks in London placed Cuba, Angola and South Africa at the same bargaining table for the first time. A joint communique issued Wednesday said they would meet again soon.

U.S. Assistant Secretary of State Chester Crocker, who served as chairman, said the session was an important step toward withdrawal of Cuban and South African troops from Angola and independence for South-West Africa, the South African-controlled territory known as Namibia.

"But it is fair to be skeptical," Crocker said. "There are big, tough issues that lie ahead."

Among those issues:

-UNITA, which was excluded from the London talks, insists that it must be included eventually. The reb-els' leader, Jonas Savimbi, is reviled by Angolan government officials, but he is a proud, self-confident commander who is unlikely to stand aside in the interests of a settlement. The United States, which helps arm the rebels, says it won't abandon him.

-Angola will not want to be seen by other Third World countries as yielding to the white-minority rulers of South Africa. Mere withdrawal of South African troops from its territory is unlikely to suffice, and Angola will probably insist on unconditional independence for Namibia.