oreign Minister Roelof (Pik) Botha returned to South Africa last night after talks with U.S. Secretary of State George Shultz in Washington and said he believed the United States stood a "50 percent plus" chance of getting Angola to agree to the withdrawal of Cuban troops based there, Washington Post special correspondent Allister Sparks reported.

South Africa has made the withdrawal of the 20,000 Cuban troops estimated to be in Angola a precondition for signing an independence agreement for Namibia, which it administers despite revocation by the United Nations of its World War I-era mandate.

The Reagan administration supports South Africa's demand, while black African states in the region back Angola's position that the two issues should not be linked.

Botha said that South Africa would be satisfied with a phased withdrawal of the Cubans and that the phases should match those already agreed on for the withdrawal of South African troops from Namibia in U.N. Resolution 435, which allows up to 1,500 South African troops to remain in Namibia during elections. Botha said, however, that South Africa is demanding that all Cubans be withdrawn from Angola by the time his country reduces its military presence to that number.