A major offensive by Vietnamese occupation troops has driven communist Khmer Rouge guerrillas from several strongholds near the Thai border, but Khmer Rouge officials insist that the reverses are only temporary and have little military significance.

In an interview last week at this jungle camp in western Cambodia, Khmer Rouge leader Khieu Samphan conceded that since mid-February Vietnamese forces have "penetrated fairly deeply in our region" and overrun positions on several hills near the Thai border about 15 miles south of here. But he stressed that these were positions the Vietnamese had lost during the previous dry season and that they were recaptured at the cost of abandoning another base farther east.

Diplomats in Bangkok said that the Khmer Rouge leader appeared to be putting a gloss on an unfavorable military situation, but that it was unclear how serious his losses were.

Western intelligences sources in Bangkok said the Vietnamese offensive was the strongest attack on the Khmer Rouge in the last two years. But they dismissed suggestions in the Thai capital that the communist guerrillas were on the verge of military defeat.

Thai military sources see the Vietnamese drive as a possible prelude to a major thrust northward to attack Khmer Rouge bases in this area before the dry season ends in May. Earlier, Thai officials said Khmer Rouge guerrillas lost two strongholds in the Khao Din hills that straddle the Thai-Cambodian border about 10 miles to the south after heavy fighting that began Thursday night. The officials said dozens of Vietnamese mortar and artillery shells landed on Thai territory, prompting Thai forces along the border to return the fire Saturday.

During a 30-hour visit ending Thursday afternoon, however, a calm in the area was broken only rarely by the distant boom of artillery from fighting said to be taking place near Phnom Makhoeun about 12 miles to the southeast.

In a wide-ranging, four-hour interview, Khieu Samphan went to great lengths to contradict recent press reports suggesting that the Khmer Rouge, driven from power in Cambodia by Vietnamese invasion forces in January 1979, were taking a severe battering from Hanoi's current offensive. He insisted, for example, that contrary to some reports, the Vietnamese had not taken the key hills of Phnom Malai, five miles south of here.

The guerrilla leader, who had returned two days earlier from a meeting in Peking with Prince Norodom Sihanouk, Cambodia's former head of state, also stressed his group's willingness to share power with Sihanouk and others dedicated to overthrowing the pro-Vietnamese government installed in Phnom Penh.

Khieu Samphan holds the titles of president and prime minister of the Khmer Rouge government known as Democratic Kampuchea, which is still recognized by the United Nations as Cambodia's legitimate government.

He described the goal of the Vietnamese offensive as "both military and political. On the military front, they are trying to dislodge us from the region to make people think they have the whole country. But they've only been able to reach this goal partially."

He added, "We dodged the bulk of their forces in order to preserve our own so we can attack them from behind and harass them with guerrilla activity. We have been doing this since mid-February, and we will pursue our harassing attacks. With the coming rainy season, we will intensify our actions."

The dry season, generally lasting from November to May, favors the 200,000-strong Vietnamese occupation force because it affords greater mobility to trucks and tanks. The monsoon season, from June to October, usually gives the advantage to the 30,000 to 40,000 Khmer Rouge guerrillas.

Khmer Rouge officials said two Vietnamese divisions and elements of two others, totaling more than 10,000 troops, have pushed into the Khao Din area since the offensive there began Feb. 18. The officials conceded that the Vietnamese had punched through to a river on the Thai border and captured a Khmer Rouge camp at Chak Rey about 18 miles south of here.

However, Khieu Samphan denied that his forces were taking heavy casualties. Western diplomats said that unless heavy losses were inflicted, the guerrillas would emerge from the offensive relatively unscathed.

"Simply giving up turf that they're going to regain in a couple of months anyway is not all that important," said one diplomat in Bangkok.

Khieu Samphan said the aim of Khmer Rouge forces was to cut Vietnamese supply lines by "annihilating transport units" and to prevent Hanoi's forces from spreading out from their recently acquired bases.

The 50-year-old Khmer Rouge leader insisted that his group was ready to join forces with two noncommunist resistance groups in a proposed coalition government. He also dismissed the idea of any compromise with Vietnam or the government it installed in Phnom Penh in 1979, and he defended the role in the current struggle of the internationally reviled Khmer Rouge strongman, Pol Pot, while indirectly confirming reports of differences in Khmer Rouge ranks.

Considered the dominant force in the Democratic Kampuchea government after the April 1975 communist victory over Cambodia's pro-American government, Pol Pot presided over a four-year reign of terror, mass murder, destruction and economic ruin in which 1 million to 2 million Cambodians died. Of this number, according to Western experts, about 200,000 reportedly were executed. The rest were said to have died of exhaustion, malnutrition or illness under the rule of the Khmer Rouge, which means "Red Cambodians."

In December 1979 the Khmer Rouge repudiated some of its harsher policies and dropped Pol Pot from the government. However, he remained in command of the National Army of Democratic Kampuchea and is still considered the regime's dominant figure.

There have been reports of differences between Pol Pot, 53, and the current Khmer Rouge government over efforts to form an anti-Vietnamese coalition. While Khieu Samphan would not comment directly on those reports, he did say, "It's true we discussed the coalition question minutely. In our search for a union, our concern is to strengthen our forces. This means in our ranks everyone has to be persuaded of the need for a union." Asked if Pol Pot were persuaded, Khieu Samphan replied said, "certainly."

Choosing his words carefully in fluent French, the silver-haired Khieu Samphan strongly rejected suggestions by anticommunist Cambodian resistance leader Son Sann that Pol Pot and certain other Khmer Rouge leaders voluntarily go into exile. Son Sann, a former Cambodian prime minister, has suggested that such a move could help make a Democratic Kampuchea government palatable to the Cambodian people.

Khieu Samphan said he could not accept Son Sann's demand because "it would be unjust . . . . Pol Pot as well as other leaders of Democratic Kampuchea have the right to stay in their own country and fight alongside our people for the liberation of our country."

Khieu Samphan stressed repeatedly that "we are ready to share our role in the Democratic Kampuchea government with other parties," despite what he said was "a very great risk" in doing so.

He was referring to efforts to put together a coalition government with the parties of Sihanouk and Son Sann, who did not to attend last week's Peking session.

Despite Son Sann's absence, Khieu Samphan said, he had agreed in Peking to "another step in the direction of rapprochement" with Son Sann by dropping a Khmer Rouge demand that "the other parties submit to the institutions of Democratic Kampuchea." Instead, he said, the coalition partners only need accept the "framework" of the Khmer Rouge government.

The Khmer Rouge leader said he and Sihanouk had not discussed the prince's view that a political settlement solution of the Cambodian issue must be reached with the Vietnamese.

"Our one and only goal is to make the Vietnamese leave our country," he said. "To reach this, it is necessary to combine both military and diplomatic actions."

He added that even if the Vietnamese eventually withdraw their forces, "they will still have designs on Cambodia." Therefore, he said, "our salvation is on the Western side. We need the West very much."