Son Sann is a thin, frail old man who walks through the forests of Cambodia's war zone supporting himself with a stick. He is a guerrilla leader, unlikely as that seems, who is stirring hope in Washington and other capitals that a third force is finally emerging in the struggle for Cambodia.

The idea of a third force in Indochina, neither communist nor corrupt, has always been attractive to the Westerns who have become involved here. Graham Greene ridiculed the notion in his book "The Quiet American" in the 1950s. Yet once again, the idea is being touted for Cambodia. Son Sann is now its symbol.

Sitting under a hurricane lamp in his well-ordered camp high in these densely wooded mountains, Son Sann talked to this reporter recently about his main concern of the moment, which is the same as the main concern of every other Cambodian: food.

Now 68 and in poor health, Son Sann was 17 times a Cabinet minister under deposed Prince Norodom Sihanouk in those halcyon days of the 1950s and '60s, when Sihanouk managed to keep war, hunger and geopolitics largely out of Camboida.

Son Sann also ran the national bank; now he sends his supporters walking through the countryside telling villagers that his Khmer People's National Liberation Front offers an alternative to both Heng Samrin and the Khmer Rouge and will organize a food distribution system for this ravaged country.

"Our first aim is to try and get food to people in the interior," he said. "We don't think people should forever be encouraged to go to the [Thai] border for rice" -- which is handed out in camps often controlled by remnants of the rightist group that overthrew Sihanouk on March 18, 1970.

After spending most of the post decade in exile in Paris, Son Sann formed his front and returned to Cambodia last year. He now controls several villages in the west of the country. At his headquarters he has about 3,000 people, including about 100 Khmer Rouge defectors.

International food aid is brought in by porters every day from Thailand; only a few miles down the mountain. Land is being cultivated. He hopes to make the camp self-sufficient in rice and vegetables by the end of the year.

In those border camps that Son Sann hopes to keep his supporters away from, another group of former officials have risen from the ashes of Cambodia and are flourishing in a corrupt commercialism that the across-the-border feeding operation has encouraged.

The Thai border village of Aranyaprathet is a boom town now, thriving off the despair and misery of Camobdia.

Since the Cambodian refugees flooded into Thailand last fall, more than 400 "farang," as foreigners are called here, have converged on the town. Doctors, nurses nurtitionists, spies administrators, engineers, "disaster groupies" -- all have been drawn to the crisis.

The local economy has been overturned. Richer Thai families have moved out to cash in. They rent their wooden homes to "farangs" for more than $500 a month.

Other Thais make other profits. Thousands of traders flock daily to the border sites and "holding centers" to sell cloth, cigarettes, food, combs and soft drinks at inflated prices to their captive market.

The Camobdians are captive many times over, to the hostilities within their own country, to the politics of Thailand, to unpredictable superpowers maneuvers, and even to those who claim to represent them.

This is evident in Ban Mouk Mouen, the terrible slum a few miles north of Aranyaprathet. This squalid corner along the border has been a magnet for Cambodians who cannot find food in their country and who have heard that free food is available from international agencies here. The American Embassy says this food has reached and kept alive a million Cambodians in recent months.

At Mak Mouen, the ghosts of Cambodias past still stalk the ground. And at Mak Mouen, the imperatives of international and Cambodian polities today intersect. It is a place where relief work by the international agencies has to coexist with intrigue and corruption.

The camp is controlled by a man named Van Saren, a 53-year-old former soldier in the army of Lon Nol, the American-backed rightist who overthrew Sihanouk in 1970. Van Saren claims to be the most "honorable" of the non communist Cambodian leaders.

In fact, he is a teak smuggler, linked closely to corrupt Thai officials. He uses the camp, littered with piles of garbage and excrement, as as base for a variety of corrupt deals.

Van Saren waalks around the camp in a pork pie hat, a large crucifix on a thick chain hanging around his neck. He is always accompanied by a troupe of young men armed with automatic rifles. A few months ago was always seen with a man who called himself (falsely) "Prince Norodom Suryavong" and claimed (falsely) to be related to Sihanouk. Journalists called him "The Mad Prince"; he has now disappeared, perhaps murdered.

In February the Mad Prince's place was taken by an eccentric American. This was a mid-30s Vietnam veteran from Arizonia named Gary Ferguson. Van Saren made him his "Minister of Defense" and called him "my son."

Ferguson strode around the camp, shouting instead of talking, with a Colt 45 stuck in his waist. He claimed that Van Saren was his "father" and father of all Cambodia. He threatened to blow out the brains of anyone who demurred.

His most fierce battles were with the doctors and relief workers of the International Committee of the Red Cross, whom he accused of doing little to help the 60,000 or so refugees crammed into the camp. Finally the Thais also grew weary of his outbursts and shipped him out of the country earlier this month.

Van Saren remains and still controls the food that he claims is intended for "the 400,000 persons here who have answered my call." He cloaks his evident gangsterism in promises to return to Cambodia to overthrow the Vietnamese-installed government headed by Heng Samrin.

Much has been made, and with good reason, of the failure of the Vietnamese and the Heng Samrin government to distribute international relief within Cambodia. But the border feeding here has been no better monitored, and there is little to suggest that the rice handed over by the relief agencies to men like Van Saren has been any more fairly shared out.

Indeed, people in the camp claim that he sells them the food they are supposed to have free. Sometimes he sells it back to the Thais, who in turn sell it again to the Red Cross and to UNICEF the next day.

There are now about 20 sites along the border at which international food is distributed by the Joint Red Cross UNICEF program. Some are controlled by Khmer Serei, others by Khmer Rouge, still others by so-called "reawakened Khmer Rouge" who claim to be altogether more gentle than before.

In many of these sites the Red Cross runs hospitals -- in some they treat wounded Khmer Rouge soldiers who then return to Cambodia to fight another day. The medical are is intermittent because Red Cross officials will not stay along the border at night.

Several voluntary agencies say they would be willing to do much more at the border if the Red Cross would let them work in camps. But Red Cross officials assert that Thailand has forbidden the organization to allow the voluntary agencies to run what amount to free-lance relief programs.

Just north of Mak Mouen there is an encampment called Nong Samet. This is run by an anti-communist Khmer Seri leader called In Sakhan, who is 39. Here health conditions are slightly better. There is less of a feeling of menace.

In Sakhan, also a former Lon Nol soldier, is a narrow-eyed man who seems rather more purposeful than Van Saren. They used to be allies; now they hate each other.

But here too distribution of supplies has been haphazard at best. And Western food taken to the Khmer Rouge encampments along the border has undoubtedly directly sustained the remnants of their army -- thus helping perpetute the group that Jimmy Carter called "the world's worst violators of human rights." Also helpful to the Khmel Rouge is medical treatment their wounded receive in some ICRC hospitals along the border.

The most successful distribution point is called Nong Chan, a few miles south of Mak Mouen. It was set up last year by yet another former officer of Lon Nol named Kong Sileah and a diligent Red Cross official named Robert Ashe. Here food has been given rather than sold to Cambodians coming from the interior. Tens of thousands of people from the interior have come and still come to Nong Chang.

It is an extraordinary, touching sight. They come with bullock carts, old bicycles and on foot. They sit under the trees waiting for the ICRC-UNICEF rice. They are given about 45 pounds each -- roughly enough to feed a family of five for a week -- and then they return into the empty interior to a silence punctuated by artillary fire.

A total of about 27,000 tons of ICRC-UNICEF rice has been brought to the border since September (as against 59,000 delivered to the Heng Samrin regime) and, the American Embassy says, been distributed to over a million people inside Cambodia.

Some Red Cross relief workers questions this figure. They say that the State Department exaggerates in order to show the Heng Samrin regime even more incompetent that it is.

Some go even furthur and say that the border feeding is not principally humanitarian but a political magnet to draw people away from their fields, from Heng Samrin control toward the resistance groups, and thus to continue the disruption of Cambodia.

Some relief workers, and some Western journalists also complain about the large number of American officials stalking the border, on political missions, but under the guise of monitoring food. U.N. High Commission for Refugees and Red Cross officials complain that the Americans think they are still in Indochina rather than on its borders, that they are trying to avenge the defeat inflicted by Hanoi in 1975. Embassy officials, however, assert that their oversight stimulats the sluggish international organizations into action.

And, whatever mixture of motives ascribed to them, the Americans can convincingly argue that the efforts they back continue to save lives. About 116,000 people, according to UNICEF, are now coming every week to Nong Chan and other sites for supplies.

But this system is precarious. The free distribution at Nong Chan undercuts Van Saren's operation and also hurts Thai officials and traders profiting from sales of free rice. At the end of 1979 Non Chan was attacked by Van Saren's soldiers and shelled by the Thai military. The attacks closed Non Chan.

The free distribution was restored in January but in mid-February the local Thai commander, Col. Prachak, suddenly ordered it stopped again. He asserted that over 60 percent of the rice being taken back into the interior was being "taxed" by the Vietnamese Army.

The American Embassy protested fiercely. When Richard Holbrooke, Assistant Secretary of State for East Asia and the Pacific, visited Thailand last month, the remonstrated with the Thais about the closure. The feeding was resumed.

But that sequence only underscored how much power an official like Col. Prachak -- a rising star in the Thai Army and though to be even better placed with the new government -- has over the precarious cross-border feeding. Despite the best efforts of the American Embassy and State Department, and even though at least half a million people are now dependent upon it, continuation of the feeding effort cannot be taken for granted.

The whole Cambodian relief effort can be at best only a temporary, time-buying proposition, one that will keep Cambodians alive long enough to arrive at a solution to their continuing political conflicts, which have grown even more intractable and horrible than Graham Greene and other prophets foresaw.

When Greene was writing, the protagonists in Indochina were involved in a struggle pitting nationalism against colonialism. There was no space for a third force. Now, nationalism has been subsumed by totalitarianism in Vietnam, and Cambodia it has been consured by Pol Pot's Khmer Rouge. In each case, nationalism has been horribly deformed. If Son Sann or other serious leaders could embody Cambodian nationalism, then there would be a possibility that their movements could yet play a significant role in Cambodia's evolution. But now, as ever in Cambodia, that evolution will be dominated by events and political priorities way beyond the control of the Cambodians themselves.