South Africa and the South-West Africa People's Organization have agreed to a formal cease-fire in Namibia beginning Saturday, a U.N. official said Thursday.

The Marxist-led SWAPO organization and the South African military have been fighting a guerrilla war in the southwest African territory since 1966 but have observed an informal truce for months.In separate letters to Secretary-General Javier Perez de Cuellar, both parties agreed to begin honoring the cease-fire on Saturday, said U.N. spokesman Francois Giuliani.

That is the date that the United Nations is to begin implementing a one-year plan to free Namibia from 74 years of South African rule, resulting in a black majority-ruled sovereign state next year.

Perez de Cuellar has informed the Security Council that he proposed the cease-fire to SWAPO and South Africa on March 14.

"South Africa and SWAPO respectively confirmed their agreement to abide by the formal cease-fire from the date and time proposed," said the U.N. chief's report to the council, read out by Giuliani.