The Palestinians' unofficial parliament-in-exile has wrapped up its business here, but there is another frustrated, embattled guerrilla movement still in town, convinced that it, too, has been thwarted by U.S. aid to its enemies.

The Polisario, which for 10 years has been fighting a variety of foes to obtain independence for the former Spanish Sahara, now confronts increasing indications that it is going nowhere diplomatically or militarily.

Founded 10 years ago, the Popular Front for the Liberation of Saguia el Hamra and Rio de Oro--as the southern and northern parts of the former Spanish Saharan colony were called--reached its high-water mark in early 1982.

Since taking up arms against Morocco in 1976, its desert warriors had inflicted defeat after defeat on the Army of King Hassan II.

In a theatrical move in 1975, when the Spanish government was only too happy to leave, Hassan started the "green march."

Hundreds of thousands of Moroccan civilians marched into the Sahara colony and declared it Moroccan. Mauritania annexed the southern third but was knocked out of the war in 1979, whereupon Morocco laid claim to the entire Colorado-sized desert land.

On the diplomatic front, the Organization of African Unity narrowly voted in January 1982 to make the Polisario's political arm, the self-styled Sahara Arab Democratic Republic, its 51st member. More than 100 countries established relations with the Polisario, and 54 nonaligned governments recognized the Sahara Arab Democratic Republic.

Then the tide turned militarily and the Polisario was stymied. Its Algerian- and Libyan-supplied arms--including Soviet-made ground-to-air missiles, which shot down six Moroccan warplanes in October 1981--proved worthless against the king's new strategy.

Hassan enclosed the useful portion of the Western Sahara--less than 10 percent of the area but holding almost all of the population and the phosphate deposits, its only riches--behind a 280-mile sand parapet as high as eight feet.

Completed last July, the defenses guard a triangle stretching from the inland holy city of Smara south to Boukra and back north to the capital of Layoun.

Life in the capital is so relaxed that Moroccan troops there, which are part of a force numbering more than 80,000, no longer carry arms in town.

What makes the wall work, according to the Polisario, is integrated radar and electronics gear provided by the United States.

Mohammed Ould Saleck, in charge of the Polisario's foreign relations, conceded that the guerrillas have not mounted any "big operations for approximately a year." But, in an interview in a Moorish villa overlooking the Bay of Algiers, he insisted, "That does not mean there won't be big battles."

"We can destroy the wall," the French- and Spanish-educated official said, but he invoked military secrecy in declining to explain how.

"Without the United States' help to Morocco we would have liberated our country," he said.

Ticking off first the Carter then the Reagan administrations' gradual shift from providing only defensive weapons not to be deployed outside Morocco proper to allowing U.S.-supplied offensive arms to be used in the Sahara, he warned that the Polisario might seek Soviet Bloc help.

He described the process as virtually inescapable. But that is a siren call that the Soviets have failed to heed over the years, presumably because of their interest in Morocco as the gateway to the Mediterranean.

The Polisario has "proof" that the United States and Saudi Arabia pressured unnamed African countries to boycott an abortive OAU summit last year in Tripoli, Libya, Ould Saleck said. Although elected to membership, the Polisario was denied a seat and "voluntarily" left, and the summit has yet to take place.

In the summer of 1981, the OAU summit conference in Nairobi, with U.S. backing, persuaded King Hassan to accept a cease-fire and a referendum on the Sahara's future.

A referendum was problematical from the start because the belligerents do not agree on the population. The Moroccans, using a 1974 Spanish census, contend that there are only 76,000 Saharans. The Polisario insists the population is 750,000.

The Polisario thesis is that U.S. support has made the king much more intransigent. "He has closed all the doors," Ould Saleck said, "and all the windows."

The payoff for the United States, he added, is access for the Pentagon's Middle East Rapid Deployment Force to the old air bases that the United States built in the 1950s but then handed over to Morocco after independence in 1956.

Ould Saleck noted "the increasing openness of use of U.S. bases in Morocco," his way of suggesting that the old bases had been reactivated despite official U.S. and Moroccan denials. He said that American officers in large numbers were acting as advisers to the Moroccan "operational chief of staff" in the Sahara.

He also indirectly conceded that recent tensions between Algeria and Libya on other matters had not helped the Polisario cause. Since Algerian President Chadli Bendjedid took office after Houari Boumedienne died in 1978, intelligence sources said, Algeria has stopped letting the Polisario use its territory to attack Morocco proper.