Just before Christmas last year, a senior official in the Vietnamese-installed administration in Cambodia joined the tide of refugees flooding across the border into Thailand. Once safe in a refugee camp he told Western relief officials a story that stunned, and disheartened, them.

This Cambodian had been highly placed in the Ministry of Commerce and had watched over the receipt and distribution of international food aid in Phnom Penh. He had represented the Heng Samrin government in meetings with foreign officials involved in the emergency relief effort.

One-half of all the international aid reaching the port of Kompong Som, the defector told Red Cross officials, was being trucked to Vietnam. Almost all of the rest was being warehoused, apparently for sale to the starving people of Cambodia once a currency had been reintroduced into that war-ruined nation.

The story of supplies withheld echoed in detail the tales of thousands of Cambodian peasants who had made the same trek and who also said that no food was being distributed in Camabodia despite the great international efforts. His story was shocking; Western officials reacted immediately.

The Cambodian defector (whose name is not being published for fear of reprisal against his family) was immediately shipped off to Paris and put under wraps. Reports of his account were marked confidential, and the relief agencies sought to keep the story from getting out.

The reaction was almost a reflex for relief officials who for several weeks had been uncomfortably aware that much of the food they were funneling into Cambodia was not reaching those for whom it was intended, but who did not want that generally known. They were aware that stories documenting this would upset their two most important constituencies -- the donors in the West, who would cut gifts, and the Vietnamese, who if attacked might halt the largest, best coordinated attempts to save Cambodians from mass starvation.

In Geneva, the International Commitee of the Red Cross now says that only a few hundred of the 26,000 tons of food delivered to Cambodia last year had been distributed from Kompong Som by the end of December. Most of the rest had been stored by the Heng Samrin authorities.

It was at that time that a teacher from Phnom Penh told a Western embassy official on the border:

"People are dying on the road and in the villages because they have no food, quietly dying of starvation."

Refugees from Kompong Speu Province were telling officials in Thailand then that 30 to 40 people a day were still dying in their district. Suicide was said to be common.

That, however, was not the picture being painted by the Vietnamese or by many journalists and relief officials allowed to visit Cambodia. They reported instead that the famine was coming under control and Cambodia was coming back to life.

Only one explanation of the different views seems possible. Both are accurate. In some parts of Cambodia, the government has been handing out food in adequate amounts. Those are the parts that the government politically controls. In other areas -- where insurgent Khmer Rouge and other anti-Vietnamese groups are active -- they have not allowed relief distribution, even if starvation results.

Relief officials and independent observers agree that the situation inside Cambodia now seems to have improved. Since the beginning of the year, the Heng Samrin government has gained confidence in the agencies and the agencies, in response to criticism from home, appear to have been more insistent on on-site inspection of food distribution.

But the accounts of refugees, including the Ministry of Commerce defector, and the embarrassed silence by relief agencies during a critical period last year suggest that the possibility for new tragedy still exists in Cambodia, which remains balanced on a knife's edge.

Speaking in December, the defector asserted that very little food was reaching the people at all, because even what was being distributed from the warehouses remained in the hands of province chiefs. He also maintained that food sometimes was "distributed" merely to deceive visiting aid officials, who wanted evidence of distribution. As soon as they had left, the food was taken back again.

The Cambodian people liked the international agencies, the refugee said, and were grateful for their help. The Vietnamese did not like them however, and considered those Cambodians in contact with them to be enemies of the party. This was why he had fled.

His alarming account came at a bad time for the relief agencies, particularly for groups such as Britain's nonprofit Oxfam, which had staked their reputations on the willingness and ability of the Cambodian government of Heng Samrin not only to receive, the but also to distribute supplies. Yet the story was not a complete surprise to them.

Through November, more and more food had been brought into Kompong Som, and then into Phnom Penh, but relief officials became uncomfortably aware that the warehouses were not being emptied at nearly the speed at which they were being filled.

In most international relief operations of the Cambodian scale, the contributing agencies expect -- or are automatically allowed -- to monitor distribution of their food and other supplies. In the case of Cambodia, Oxfam, bowiwng to the political concerns of the Heng Samrin government, consciously had waived this right. The Red Cross and UNICEF had, in effect, made similiar concessions, though less publicly. They also had agreed to run their programs with very small staffs -- Oxfam had seven people in Phnom Penh; Red Cross-UNICEF had 12.

In late November, a furious debate erupted in the Western press. Were the Vietnamese and the Phnom Penh governments now withholding the food they had allowed to be sent -- or even diverting it to Vietnam?

Vietnam was experiencing its own food shortage, and some charged that the food was simply unloaded in Cambodia, then trucked eastward across the Vietnamese border. Others said the Vietnamese were using the food as a political weapon inside Cambodia, withholding it from those who lived in zones still controlled by the Khmer Rouge.

The State Department announced its belief that the hold-ups in distribution were indeed deliberate. Francois Ponchaud, a French Jesuit who had diligently chronicled the destructiveness of the Khmer Rouge in his book "Cambodia, Year Zero," maintained that the Vietnamese were conducting a "new, subtle genocide" against the Cambodian people.

International aid officials hastened to disagree. On the contrary, they said, they had no evidence of deliberate obstruction by the Phnom Penh or Vietnamese authorities.

Malcolm Harper, Oxfam's man in Phnom Penh, said he was confident that aid was beginning to reach those for whom it was intended.

Oxfam also acknowledged, however, that its ability to make any real inspection of distribution was limited. Its aid was simply handed over to the relevant government ministry, and only occasional on-site inspections were permitted. Fortnightly reports were supposed to be submitted to the agencies concerned; Oxfam acknowledged the first of these reports to be "useless."

The aid officials argued that any shortcomings in distribution were because of logistical problems -- the inevitable result of Khmer Rouge destruction. There were no forklift trucks at the airport; no cranes at Kompong Som. The few officials in Phnom Penh's skeletal government had almost no idea of how to handle large quantities of supplies.. All planes and boats had to be unloaded by a weak and unskilled labor force.

The railway from Kompong Som to Phnom Pehn was inefficient; the roads often were impassable because of the lack of bridges and repair. A journey that had taken a few hours before the war now took several days in many cases.

"Building up the transport capacity was a very serious and rather lengthy problem," said Jacques Beaumont of UNICEF, who is now back in New York. Like other aid officials, Beaumont tends to blame physical rather than political constraints for the slowness of food distribution at the end of last year.

Refugees, however, continued to tell a very different story.

They spoke of theft by the Vietnamese and said they sometimes were sold, rather than given, food provided free by the international agencies. Many said that the Soviet corn was much more widely available than Western rice, but that it was of poor quality and required hours of boiling before it was edible.

Since 1975, when they first began to talk of Khmer Rouge atrocities, Cambodian refugees to Thailand have told alarming stories about conditions in their country. Their descriptions of Khmer Rouge behavior were found to have been largely accurate.

International relief agencies have two responsibilities: to the starving people they are supposed to assist, and to their donors -- in Oxfam's case the hundreds of thousands of British schoolchildren who had sold their toys to send food to Cambodia.

To try to feed Cambodians, the agencies had accepted unusual restrictions and conditions on their operations. Once inside Cambodia, they were loath to acknowledge that their efforts were being undercut by the government in charge. To be able to stay, they apparently felt that they were not free to voice their frustrations openly.

Food does now appear to be more widely available than before Christmas.

The agencies remain cautious, however. Although many aid officials publicly criticized the February "March of Survival" organized by groups such as the International Rescue Committee and Joan Baez's Humanitas to protest poor food distribution, these same officials said privately that such continued pressure helped them make their point in Phnom Penh.

Although much more food seems to be leaving the warehouse of Kompong Som and Phnom Penh, there is now a dispute among aid organizations as to just how much food actually has been sent. According to the World Food Program, which is responsible for purchasing and shipping the food for the Red Cross-UNICEF effort, 59,000 tons had arrived in Cambodia by the end of February. But J. P. Hocke, the director of the Red Cross operations, said recently that the figure was only 38,000 tons.

There figures have bearing on similar discrepancies in the amount of food actually shifted from the warehouses into the countryside. At the end of February, UNICEF in Bangkok declared that 26,000 tons had been distributed between Jan. 14 and Feb. 14. A few weeks ago, the Red Cross said that about 27,000 tons had been distributed between the end of October and the end of February.

Whichever figures one accepts, they confirm that distribution of food until the end of 1979 was minimal.

Inevitably this poor distribution killed many Cambodians. How many is not known. The original fears for "2 million dead by Christmas" may have been exaggerated, but one U.S. analyst now reckons that at least half a million people died of famine last year.

In January, new UNICEF director Jim Grant, visited Cambodia and pronounced himself very impressed with progress made in distribution. Grant was especially encouraged that the authorities had allowed the wet season rice harvest (only about 15 percent of a normal year's crop) to remain in the villages.

Journalists who have visited Cambodia in recent weeks also have been impressed. Cambodia, they feel, is combing back to life under the Heng Samrin government. Yet refugees continue to tell of food being withheld, and thousands keep coming to the Thai border for supplies.

On one thing there is agreement: famine will recur on Cambodia unless a decent crop is planted and harvested this year. For this international supplies of seed and food must continue, and be adequately distributed, until at least the end of 1980. Otherwise the disaster will be repeated.

The poverty of Cambodian society today cannot be blamed on the Vietnamese.

It is the product of 10 years of disruption and war and, in particular, of four years of rule by the Khmer Rouge. But at the same time, the Khmer Rouge cannot be blamed forever for the continuing problems of Cambodia.

There is no doubt that the Heng Samrin government is far more benign than that of the Khmer Rouge's Pol Pot. But questions about Vietnamese intentions remain.

Why did they wait until July, six months after taking over Cambodia, to appeal for help? Is paranoia over Western intentions toward them an adequate excuse for restricting the size of relief teams allowed into Phnom Pehn? Is the destruction of the infrastructure by the Khmer Rouge sufficient explanation for the disparities in distribution? Most important, perhaps, why has it taken so long for them to put together an effective Health Ministry?

Throughout 1979, the Heng Samrin government asserted that all but 50 of the 500 doctors formerly in Cambodia had been murdered by the Khmer Rouge. In any case, it was apparent to all visitors beginning last summer that medical care was dreadfully inadequate.

Yet the Ministry of Health remains one of the most ineffective government agencies in Phnom Penh. Its tiny staff spends much of its time receiving foreign delegations. In early December, Oxfam officials in Phnom Penh complained that the "January 7" Hospital still had no supplementary feeding facilities, even though there were plenty of supplies in Phnom Penh.

The government's refusal to allow an army of Red Cross bureaucrats into Cambodia may be explained by suspicion about Western intentions. But does this explanation also justify the government's refusal to allow Western doctors and nurses into the country? Since early last year dozens of groups -- including Medecins Sans Frontieres, a French medical group that sends personnel all over the world -- have sought to come and help. They have been consistently refused. It was only last month that the Red Cross was allowed to bring 10 Soviet, five Hungarians and six Polish doctors and nurses into the country. Four East Germans are said to be on the way. Even when the 60 Vietnamese medical personnel and a Cuban team that have been in Cambodia since last summer are added, this is a very, very small, number for an exhausted, sick, starved population now though to number around 5 1/2 million. It is hardly indicative of a government which adequately cares for its people.