Angolan President Jose Eduardo dos Santos has proposed a timetable that over a three-year period would remove 20,000 of the Cuban troops who have been guarding his country's southern region from South African soldiers present in Namibia and part of Angola, the Manchester Guardian reported yesterday.

The proposal, which the newspaper reported was made in a letter sent yesterday to United Nations Secretary General Javier Perez de Cuellar, is more specific than any previous Angolan plan for a Cuban pullout.

At the same, however, it sets several rigid conditions that must be met before the withdrawal could begin and appears to mark a toughening in the Angolan president's bargaining position for a peace settlement in southern Africa.

The letter apparently makes no reference to a complete pullout of Cuban troops, which are estimated to total about 25,000.

As described by the Manchester Guardian, dos Santos' letter expands on an Angolan-Cuban proposal, first made two years ago, that called for implementation of a U.N. peace plan in Namibia.

That plan, known as U.N. Resolution 435, mandates the establishment of a U.N. peace-keeping force in Namibia and the withdrawal of all but 1,500 South African troops from the country.

The letter reportedly also reiterates a recent Angolan demand that South Africa end support for guerrillas who now control large portions of southern Angola, the newspaper said.

The guerrilla group, known as UNITA, is led by Jonas Savimbi, who demands a role in negotiations for a regional peace settlement in southern Africa. UNITA -- which stands for National Union for the Total Independence of Angola -- recently has stepped up sabotage attacks in Angola.

In the Angolan government's view, the main obstruction to progress on peace talks in the past has been a joint U.S.-South African precondition that all Cuban troops in Angola be removed before Namibia -- which South Africa controls in defiance of a U.N. mandate -- can become independent. Differences over this issue of "linkage" with the Cubans have stalled negotiations for more than two years.

The Angolan president's letter reportedly "categorically rejects" linkage between a Cuban troop pullout and implementation of the U.N. peace plan in Namibia. But the overall effect of the letter appears to be to spell out that linkage. For the first time, it provides a timetable for the withdrawal of South African and Cuban troops.

Dos Santos's new proposal reportedly also demands a cease-fire between South Africa and the South-West Africa People's Organization (SWAPO), the Namibian insurgent movement.

According to the Angolan president's plan, that cease-fire and the establishment of a U.N. force would be the cornerstone of peace. "U.N. authorities would be charged with the responsibility for verifying the dismantling of the UNITA bases on Namibian territory," the letter reportedly says.

The letter reportedly says publicly for the first time that 20,000 Cuban troops are deployed on the southern defense line that runs along the 15th Parallel between the towns of Lubango and Menongue.

With U.N. troops in place in Namibia, and the South African Air Force and all but 1,500 infantrymen withdrawn, Angola has offered to pull 5,000 Cubans out within four months. "As a gesture of good will," the letter says, the other 15,000 would be pulled out within three years in three separate batches.

The letter also reportedly spells out the Angolan government's concern about a continuing threat from the north, although Zaire is not mentioned. The letter says Cuban troops are guarding the Cabinda oil area, which borders Zaire. "Aggressions from the north and northeast, especially against Cabinda, have already happened," it says.

No figure is given for the Cuban troops in Cabinda, or for elsewhere in the north, in the east or in Luanda itself. Diplomatic observers report that there are between 2,000 and 3,000 troops in the Cabinda area. The letter reportedly makes it clear that no timetable will be considered for the withdrawal of Cuban troops in these more northern areas except as negotiated between Cuba and Angola.

The letter says the remaining Cubans, however, will not be deployed south of the 13th Parallel. That line corresponds with the area occupied by South African forces from 1981 until their partial withdrawal this year.

In a related development, South Africa announced this week that it will hold a ministerial-level meeting with Angola soon to set a date for completing its troop withdrawal from Angola.