The government of Prime Minister Prem Tinsulanond is coming under growing pressure to extend the tenure of Army Commander Gen. Arthit Kamlang-ek amid tensions within the armed forces, according to Thai military sources.

The pressures mounted last night with an unusual news conference in which two senior Army generals publicly called for Arthit's term to be extended for a second consecutive year. They said rejection would amount to "a reversal against the will of the armed forces" and issued a cryptic warning to the government to resolve the matter within the coming week.

"The weather is now getting hot, but it will be hotter next month and people can easily become restless," said Gen. Chuthai Saengthaveep, the deputy Army commander and a strong supporter of Arthit. "So everything should be settled this month."

Arthit yesterday criticized "academics" who he said opposed his extension. The general said Thailand would suffer an "economic loss" if his retirement, now scheduled for Aug. 31, were not put off again.

The statements, and the underlying factionalism in the armed forces, have raised new anxieties about the prospect of a military coup in a country that has seen 15 such takeovers or attempts since 1932. On Sept. 9 last year, a coup attempt left at least five persons dead -- including two NBC television journalists -- and 59 wounded. It was the second unsuccessful military effort to oust Prem, himself a former general, in four years.

Forty of the alleged plotters, among them a former prime minister and four other retired senior officers, have gone on trial, but the case has done nothing to lower tensions or remove existing rivalries in the armed forces, military sources said.

So far Prem, who also holds the post of defense minister, has taken no action on demands for Arthit's extension, but a decision is expected shortly. The Thai military has a mandatory retirement age of 60, and annual retirement lists are usually issued in April.

"These days are very tough for Gen. Prem," said a senior Thai officer who is neutral in the current dispute. He described a cat-and-mouse game in which Arthit and his chief military rival, Army Chief of Staff Gen. Chaovalit Yongchaiyuth, were each jockeying for position and trying to lure the other into a false move.

Another extension for Arthit, whose scheduled retirement last year was postponed amid controversy, is seen as potentially fatal to the career of Chaovalit, who was one of Prem's strongest supporters in putting down the Sept. 9 coup attempt. Chaovalit, who is not due to retire until 1992, moved into position to succeed Arthit as commander in chief of the 160,000-strong Thai Army, the most coveted military post, when he was promoted to his current position as chief of staff last October in an annual military reshuffle.

Arthit, who concurrently holds the title of Armed Forces Supreme Commander, was instrumental in crushing an April 1981 coup attempt against Prem. However, he has since fallen out with the 65-year-old prime minister and former Army commander, who came to power in 1980 through a constitutional process. In an appearance with other dignitaries yesterday at Bangkok's airport to see off Princess Sirindhorn, the two men did not speak to each other, Bangkok newspapers noted.

Although he has not commented publicly on the matter, Prem is understood to favor Arthit's retirement, military sources said.

Arthit himself occasionally has expressed bitterness about opposition to his extension. Earlier this month he challenged the government to tell him so if it "does not want me." If the government felt that way, he said, it should "summon me and say that I should tender my resignation because I am a troublemaker, I have many enemies and obstruct the democratic process." In that case, Arthit said, "I will immediately write the resignation letter." He added, however, that he thought his only enemies were "those who embrace communism or subversive elements."

In recent days, Arthit has held a series of "dinners" at his house, attended by dozens of battalion commanders and other key military officers. Arthit's allies have portrayed the gatherings as shows of support for the Army commander's extension, but some officers invited reportedly have expressed mixed feelings.

If the issue should come to a head militarily, Arthit could count on the support of the First Army Region commander, Lt. Gen. Pichit Kullavanich, who was passed over in the last reshuffle, and a number of infantry commanders, military sources said. According to one well-placed general, Chaovalit probably could count on the Army's Special Warfare Command under Lt. Gen. Soonthorn Kongsompong, one of Chaovalit's academy classmates.