US role in Namibia too open-ended?

The death of two American diplomats in Namibia has made tangible the risks the Reagan administration assumed in agreeing to play a role in a cease-fire between South Africa and Angola.

The weakness of the agreement from the start has been that it does not involve the SWAPO guerrilla movement, which is fighting for Namibia's independence from South Africa. SWAPO's base camps are in Angola.

SWAPO (the South West Africa People's Organization) is believed to be responsible for the deaths Sunday of the diplomats and two local residents. The rebel group's exclusion from the cease-fire process has meant that its sabotage campaign within Namibia has continued.

The United States diplomats killed were apparently the victims of a SWAPO attack at a gas station near Oshakati, Namibia. A South African source said there was no indication yet whether the attack was directed at the Americans.

The Reagan administration had sought a low profile for its involvement in Namibia. This attack may undo that status and increase pressure for a more carefully defined US role in monitoring the cease-fire. When the agreement was worked out in February, the US agreed to play a small but apparently open-ended role in monitoring the cease-fire.

The exclusion of SWAPO from the agreement also poses another, and perhaps greater, risk for the Reagan administration: that the South African-Angolan agreement, which calls for a ''disengagement'' of Pretoria's forces from Angola and a cease-fire, will not bring Namibian independence closer. The Reagan administration could become enmeshed in a longer-term role in Namibia than it bargained for, say political analysts here.

The Reagan administration was aware of these risks at the outset. But diplomatic sources concede the recent deaths may increase pressure for redefining the US role.

One thing that remains unclear is what the US role will be once the disengagement is complete. From an office in Windhoek, the US has been monitoring the disengagement and the terms of the cease-fire, which require that as Pretoria withdraws, Angola will not permit SWAPO to move back into the vacated area.

Even after Pretoria has withdrawn its forces, it will continue to insist that SWAPO not be allowed back into southern Angola. This means there could be a continuing role for the US monitoring office after disengagement, analysts point out.

When the Reagan administration agreed in February to a small monitoring role, it said in a statement with Angola and South Africa that the cease-fire and disengagement were an ''important step'' toward regional peace and Namibian independence.

The Reagan administration is pushing for further negotiations to maintain momentum toward Namibian independence when the disengagement of South African forces is completed in the next several weeks, diplomatic sources say.

But the next steps could be the toughest. The estimated 25,000 Cuban troops in Angola must be withdrawn as part of any settlement in Namibia. Angola is locked in its own civil war, making the exodus of the Cubans difficult for Luanda absent some internal settlement in the country, say some analysts.

Meanwhile, SWAPO says it will carry on its ''armed struggle'' within Namibia until South Africa is ready to enter serious negotiations aimed at granting the territory independence.

The US diplomats killed in the bomb explosion were Dennis Keogh, director of the monitoring office in Windhoek, and Lt. Col. Kenneth Crabtree, a military adviser in the same office.

The US State Department says the two men were in the Namibian operational zone to be briefed by the South African Defense Force on the disengagement process. Such briefings were apparently routine. At no time, said a US Embassy spokesman here, have the US officials from Windhoek gone into Angola as part of the US monitoring function.

The liaison office in Windhoek flies no US flag and its entrance is in the back of a building. It has been staffed by about seven people. Keogh, a former political counselor in South Africa, was sent from Washington a few weeks ago for a 30-day assignment.

Looked at it in narrow terms, the disengagement process appears to be proceeding well. Before this incident, a spokesman in the liaison office in Windhoek said the disengagement was going slower than expected but that this was a good sign. Both Angola and South Africa were implementing the agreement thoroughly and methodically. Indeed, joint South African-Angolan forces have been involved in clashes with SWAPO in Angola.

As the troop disengagement proceeds, a joint monitoring commission of Angolans and South Africans moves its headquarters steadily southward in Angola. The commission started in Cuvelai, about 120 miles inside Angola. Pretoria has announced that the commission will shortly move to Evale, about 60 miles inside Angola, meaning the disengagement is approximately half way complete.

The State Department in Washington says it has no intention of terminating its monitoring function in Windhoek as a result of the deaths.