Vietnamese troops fought a brief battle with Thai forces yesterday as Hanoi's current offensive against Cambodian resistance guerrillas spilled across the Thai-Cambodian border, Thai military officials said today.

At least one Thai soldier was killed and nine were wounded when Vietnamese troops crossed the border near the Cambodian resistance settlement of O Bok in northwestern Cambodia and clashed with a Thai patrol, the officials said.

In a separate operation on the northern Cambodian border, Vietnamese gunners poured heavy artillery fire into a resistance base opposite Thailand's Nam Yuen district today, according to Thai Army spokesman Maj. Gen. Naruedol Detpradiyuth. The shelling sent a number of Cambodian refugees fleeing across the border into Thailand and forced hundreds of Thais to evacuate nearby border villages, he said. Information on casualties was not immediately available.

The Vietnamese attacks, the latest in a dry-season offensive against Cambodian guerrillas battling Vietnam's occupation of Cambodia, were seen here as part of an emerging strategy to stop resistance infiltration into the Cambodian interior and continue the campaign against the guerrillas into the wet season, which begins in June.

"It looks like the Vietnamese strategy is to try to control the important passes" along the Thai-Cambodian border and to remain in position in or near the resistance settlements to put a stop to guerrilla movement into interior provinces controlled by the Phnom Penh government, a western diplomat said.

Two key passes are near O Bok, a camp run by the anticommunist Khmer People's National Liberation Front about 12 miles north of the front's military headquarters at Ampil, and at Nam Yuen, another Khmer front camp about 120 miles to the east. About 2,000 Cambodian civilians have already been evacuated from O Bok in anticipation of more Vietnamese attacks there, western relief officials said.

Yesterday, about 23,000 Cambodian refugees moved from the outskirts of the Ampil camp to a site about two miles inside Thailand because of fears that the Vietnamese will launch an assault on the camp to coincide with Monday's sixth anniversary of their capture of Phnom Penh. Vietnamese forces invaded Cambodia in December 1978 and ousted the Khmer Rouge communist government the following month, replacing it with an administration under Heng Samrin, a Khmer Rouge defector.

According to western diplomatic sources, 5,000 to 6,000 Vietnamese troops backed by armor and artillery and supported by 800 to 1,000 Cambodian government soldiers now are poised opposite Ampil.

Thai military officers said the Vietnamese have about a dozen Soviet-built T54 tanks in position to spearhead an assault.

In a separate action, Khmer Rouge guerrillas battled Vietnamese troops to a standstill Saturday in the hilly area where the borders of Cambodia, Laos and Thailand meet, The Associated Press, quoting a Thai official, reported.

The battle began early Friday and lasted more than 30 hours, Charoensook Silabhundhu, governor of Ubon Ratchathani Province, said. The Khmer Rouge took advantage of their superior knowledge of the territory to counter effectively with mortars and small arms, he said.

In an indication of a tougher Vietnamese attitude toward the resistance, Hanoi's ambassador to the United Nations, Hoang Bich Son, said at a news conference in New York Thursday that the offensive against the guerrillas would continue through the year, not just the current dry season, from November through May. He said that Cambodian refugee settlements on the border with Thailand are nothing but "guerrilla military bases."

He also maintained that Phnom Penh government troops had made great progress in 1984 and now were in the front lines of the fighting against the resistance groups.

Continuing to build up the Phnom Penh government and Army while stopping guerrilla infiltration are considered vital to the success of elections scheduled for next year by the Heng Samrin administration and the eventual withdrawal of Vietnam's 160,000 to 180,000 occupation troops.

"There has certainly been an improvement in guerrilla capabilities in the past few years," a western diplomat said. "But to be credible they have to give the Vietnamese problems in the interior."

He said many little-reported guerrilla operations occur in the interior, carried out notably by the communist Khmer Rouge. But he said the noncommunist resistance groups -- the Khmer front led by Son Sann and a faction loyal to former Cambodian ruler Prince Norodom Sihanouk -- needed to become stronger there to induce the Vietnamese to negotiate a settlement.

Another Vietnamese measure to secure the interior, and possibly one of the reasons for the current stepped-up dry season offensive, is the construction of a barrier parallel to the Thai-Cambodian border west of the town of Sisophon, diplomats said.

According to refugee reports, they said, large numbers of Cambodian villagers have been put to work by Vietnamese forces in recent weeks to cut through jungle and build roads for the project.