Thai Army Commander Prem Tinsulanond has emerged as the likely replacement of Gen. Kriangsak Chamanan, who resigned as prime minister early today under heavy pressure from parliament.

Gen. Prem, 59, is considered certain to be chosen when the parliament meets next week, according to Thai and diplomatic sources. He has no experience in civil administration but the Thai Royal Army, through coups and countercoups, has dominated politics with few interruptions since the absolute monarchy ended in 1932.

Thailand is the United States' closest ally on the Southeast Asian mainland. Diplomats here expect the new government to review those policies, warmly endorsed by the United States, that have allowed hundreds of thousands of Indochinese refugees to find havens on Thai camps.

Gen. Kriangsak faced possible censure for allegedly mismanaging the economy and for his "open-door" refugee policy. The United States cooperated closely with his government in refugee relief work and supported its demands that Vietnam withdraw its troops from Cambodia -- an invasion that added to the refugee population.

Prem is lean, strikingly handsome and has a reputation for personal honesty.

He had long been tagged as the eventual successor to Kriangsak, who first took power in a bloodless coup in 1977.

Students of Thai politics said Kriangsak was the first military ruler to relinquish power in response to a challenge from parliament. However, behind-the-scenes erosion of support from Kriangsak's military colleagues appears to have figured in his decision, too. Prem's expected appointment is taken as evidence that many Thais still view the military as the only hope for national unity.

Kriansgak's popularity in parliament and on the street has diminished over the past year, largely due to 20 percent inflation and officially, ordered price rises for gasoline, electricity and telephone service. Thais began to turn toward Gen. Prem.

The two generals denied repeated reports of imminent coups or personal rifts. Prem avoided taking public stands on specific issues, diplomats noted, building an image as a man above petty politics and devoted to professional soldiering.

"In retrospect, his studious fence-sitting might have been the only way he could get to power without turning his back on his old friend Gen. Kriangsak or democratic principles," said one Western diplomat. It also means that very little is known about Prem's ideas of government

Diplomats noted, however, that many senior Army officers are dissatisfied with Kriangsak's refugee policies. Last fall he announced that any Cambodians coming to Thailand would receive food and shelter until conditions at home improved sufficiently to allow their return. About 400,000 newly arrived Cambodians are currently in camps in Thailand or along the border. Other Thai centers hold 140,000 Indochinese who arrived prior to 1979.

With ill-disciplined resistance groups mixed in their ranks, the refugees pose a security risk, many officers feel, and could drag Thailand into a confrontation with Vietnamese troops operating in Cambodia.

Opposition politicians often charge that the refugees' presence further strains the economy, even though the United Nations reimburses Thailand for most of the food and shelter and buys millions of dollars of supplies inside the country. Refugee policy was listed by the opposition parties ordering the censure vote as one of five major objections to Kriangsak's government.

"The burden is too heavy on Thailand. The risks are very great," said Thanat Khoman, leader of the opposition Democratic Party. Gen. Prem's feelings on the refugee question are not known, but his debt to the opposition parties could mean the views of Thanat and others will be more closely heard. Many diplomats feel the whole refugee issue will come under review.

Prem's appointment is not expected to alter military cooperation with the United States. Like most Thai officers, he is regarded as "pro-American," having made his career in a military establishment that has been bolstered by more than $1 billion in U.S. aid since 1951.

The new government's first priority, however, will be the economic strains that sparked the current crisis. Three weeks ago Kriangsak announced steep increases in the price of gasoline, cooking gas and diesel fuel, the second rise in seven months.

Since he holds the finance portfolio himself, Kriangsak was blamed personally in ensuing demonstrations for bungling the economy. At one rally of 20,000 people, an actor depicted the prime minister as a fool engrossed in his pipe and bottle of brandy.

Kriangsak's surprise resignation was not the first time he stepped out of the typical mold of a Thai military strongman: he did not use his time in power to enrich himself enormously. He allowed freedom of expression and tried to improve relations with neighboring communist governments.

Having spent most of his career in military planning offices rather than field commands, he never acquired a large group of proteges to support his future political undertakings -- a standard asset of previous military leaders. f