Failure Feared for W. Sahara Truce : United Nations: A little-known peacekeeping operation is in trouble at a moment of concern about cost of such programs.

Many diplomats and officials fear that a little-known U.N. peacekeeping operation in Western Sahara is heading toward embarrassing failure at a time when the United Nations is dispatching far more expensive, ambitious forces of peacekeepers to Yugoslavia and Cambodia.

The problems of the program in Western Sahara, a disputed region of northwestern Africa, could add to the discontent in Congress over the accelerating cost of U.N. peacekeeping programs. The United States is assessed 30% of peacekeeping costs under U.N. rules but is far behind in paying what it owes.

The Sahara operation seems to be foundering on the intransigence of King Hassan II of Morocco, which claims the region and exercises de facto control over much of it, and a growing loss of confidence in the United Nations by the Polisario Front, which seeks to make an independent nation of Western Sahara, a former Spanish colony.

The problems have been exacerbated by the evident unwillingness of the United States to put much pressure on King Hassan, an ally, who analysts believe could lose his throne if Western Sahara were to win independence from Morocco.

Underscoring the nettlesome nature of the problems, U.N. Secretary General Boutros Boutros-Ghali reportedly failed in the last few days to win approval for his nomination of Vernon A. Walters, a former U.S. ambassador to the United Nations, as head of the Western Sahara operation.

Reflecting the general embarrassment over the operation, the State Department recently refused to let the deputy military commander of the peacekeepers, an American colonel, testify at an open congressional hearing.

In a recent report to the Senate Foreign Relations Committee, based on a fact-finding trip to Western Sahara, George A. Pickart, a committee staff member, concluded that “the United Nations peace plan for the Western Sahara is in serious jeopardy.”

Boutros-Ghali has asked the Security Council for another three months to try to get the peace plan on track. The council is expected to grant the request next Friday, but there is little optimism here that the delay will make a difference.

At issue, after 16 years of guerrilla warfare, is a referendum on self-determination, scheduled for last January but postponed indefinitely. King Hassan has made it clear that he backs the referendum only if its results favor Morocco.

“I have, from the beginning, said that we would accept the results of the referendum, because the Sahara can only be Moroccan and nothing but Moroccan, whether or not there is a referendum,” the King said in a speech last year. Most outsiders believe Morocco now has the upper hand in the conflict with the Polisario Front that has cost 6,000 to 13,000 lives.

The conflict is rooted in what was known as the Green March of November, 1975, when King Hassan ordered his troops to lead a mass of 350,000 civilians across the border into the Spanish Sahara to seize the territory for Morocco. He acted despite a ruling from the World Court that Morocco was not entitled to sovereignty over the Spanish colony.

Spain had been preparing a referendum in the sparsely populated desert region to see if the Sahrawis, as the people are known, wanted independence. But Spain was in no mood to resist the Green March. Spain’s dictator, Francisco Franco, lay near death, and his government, according to some scholars, favored the Moroccan claim. Spain decided to divide the colony between Morocco and another claimant, Mauritania.

Supported by Algeria, Polisario, a Sahrawi rebel organization, started a war for independence. Years of battling drove Mauritania to give up its claim in favor of Morocco.

Building a 1,200-mile sand wall, known as a berm, around the three main Saharan cities of Laayoune, Bou Craa and Smaara, Morocco managed to pen the Polisario guerrillas into a small area between the berm and the Mauritanian and Algerian borders.

But the Moroccans could not dislodge Polisario, and a stalemate developed that culminated in a U.N.-brokered cease-fire agreement in 1990.

Under the U.N. operation, which began last September, the peacekeepers, now numbering 375, are charged with supervising the truce and validating voters for the referendum. The voter list was to be based on the Spanish census of 1974 listing 74,000 eligible voters. Although both sides accepted this in principle, Moroccan acceptance dissipated in practice.

King Hassan moved 37,000 potential voters from Morocco into tent cities in Western Sahara, then presented the U.N. peacekeepers with a list of 120,000 voters, besides the 74,000 in the original Spanish census. This infuriated Polisario and shocked the peacekeepers.

In an attempt at compromise, former U.N. Secretary General Javier Perez de Cuellar proposed last December that the original list be expanded to include all those missed in the 1974 census, the children of anyone on the list, and any Sahrawi now in Morocco who could prove six years continuous residence or 12 years nomadic residence in Spanish Sahara before 1974. The Moroccans accepted Perez de Cuellar’s plan, but Polisario rejected it as a gateway for Morocco to flood pro-Morocco voters into Western Sahara.

Although there has been no shooting between the two sides, Boutros-Ghali has accused Morocco of numerous violations of the cease-fire by moving troops, flying planes over the region, laying minefields, digging anti-tank ditches and building such fortifications as bunkers and sand walls.

Until recently, Morocco also has hindered the U.N. operation by holding up support equipment for many months in customs at the Moroccan port of Agadir.

The Western Sahara peacekeeping operation, scheduled to include 1,695 military and civilian observers at full strength, is budgeted at $181 million. Reports of its problems come at a time when members of Congress are questioning the high costs of the $1.9-billion Cambodian and $634-million Yugoslav peacekeeping programs.