Relief agencies coordinating emergency shipments of rice seed to Cambodia say they are "cautiously optimistic" that enough paddy land is being planted to move the country toward self-sufficiency in food next year.

However, shortages of farming tools and fertilizer and attacks by Khmer Rouge guerrillas could keep the main harvest this autumn below target. Cambodia would then remain at least partially dependent on foreign food aid in 1981.

With the monsoon rains, farmers working in flooded fields of bright green rice seedlings are a common sight along Cambodian highways, Westerners returning from the country report.

"One travels though the countyside and sees literally hundreds of thousands of hectares of rice coming up," said UNICEF Executive Director James Grant, who has just completed a tour of Cambodia. UNICEF and the International Red Cross direct the Western relief effort.

In the past four months, Western-financed groups have delivered more than 30,000 tons of seed to the Vietnamese-sponsored Heng Samrim government, while Vietnam has reported providing 10,000 more.

Caravans of ox carts coming illicitly to the Thai border, meanwhile, picked up 23,000 tons for distribution through private channels.

Refugees arriving in Thailand last month said that "solidarity teams" organized by the Heng Samrin authorities were busy planting rice seedlings in western provinces. In Phnom Penh, government ministries were reportedly being ordered to grow rice of their own.

Heng Samrim officials have asserted than 70 percent of their government's 3.5 million-acre target has been met.Reaching that target could mean Cambodian fields would cover all of the country's food requirements in 1981.

However, many relief officials reject Phnom Penh's claims as unreliable and are reserving judgment. "There are still large vacant areas of farmland where nothing is happening," one rice specialist commented.

Guerrillas loyal to the deposed Khmer Rouge regime appear to be stepping up their attacks under cover of the rains and could force farmers to abandon fields in isolated areas.

Buffaloes, ploughs and fertilizer are in short supply in most villages. Moreover, some relief sources have questioned the wisdom of including in the seed program large quantities of so-called "miracle rice" seed purchased in Thailand and the Philippines.

While these strains are potentially more productive and faster to mature than traditional varieties, critics argue that they are easily killed by flooding, require high soil ferility and need special tending techniques with which Cambodian farmers are not familiar.

In Kompong Speu a drought is threatening rice seedlings planted recently, relief sources said. In a few districts farmers have prepared their fields for cultivation, then found that the government did not provide seed as promised.

However, relief officials generally agree that most farmers have adequate supplies of seed. Unofficial "land bridge" shipments across the Thai border have flooded western Cambodia with seed. And Phnom Penh has distributed seed shipped to it with a speed previously unknown.

When it first arrived by air four months ago, many people feared it would pile up in warehouses, like much of the flood shipped earlier.

Foreign agencies hope the seed distribution foreshadows improved cooperation with Phnom Penh, which has generally considered them to be representatives of unfriendly governments.

Completion of seed shipments is being delayed by export problems in Thailand. Although the cause remains unclear, some relief sources feel that the Thai government is withholding the final quantities to show its displeasure over the Vietnamese incursion into Thailand in June.

Meanwhile, agency officials stress that despite the promise of a good harvest, Cambodia urgently needs 100,000 tons of food rice in the coming four months. But increasing quantities of food shipped through Phnom Penh are reaching the village level, they say.