HANOI -- Fifteen years after the end of the Vietnam war, a California-based group of Vietnamese exiles inspired by the collapse of communism in Eastern Europe is trying to ignite a guerrilla war in the southern part of this country and topple the Communist leadership here, Vietnamese officials say.

Thirty-eight suspected rebels went on trial yesterday in Hanoi's Supreme Court, focusing attention on the most recent of what the government has described as at least three abortive attempts in recent years by the exile group to infiltrate armed insurgents into Vietnam's central highlands.

In August 1989, 68 Vietnamese recruited by the so-called National United Front for the Liberation of Vietnam from refugee camps in Thailand crossed into neighboring Laos but soon ran into forces of the Hanoi-backed Laotian government, according to military and government officials here. Twenty-nine of the intruders were killed in a series of firefights spanning more than a month, 38 were captured and one escaped, the officials said.

The 38 prisoners, extradited to Vietnam in January, are being tried on charges of treason and attempting to overthrow the government. A prosecutor said without elaborating that the men received uniforms, weapons and military training from a Thai intelligence agency.

The National United Front, which is based in San Jose, Calif., was formed in 1980 by former officers of the South Vietnamese armed forces and is funded by "overseas Vietnamese" who fled the country after Hanoi's 1975 defeat of the U.S.-backed government in Saigon, officials here say.

In July, the group began publishing an anti-Hanoi newsletter called Vietnam Insight, which describes the front as a "mass organization to free Vietnam from the Vietnamese Communist regime and build a democratic and prosperous country." The front's "liberation strategy" is based on "mass mobilization," with military action "conceived as supplemental," the newsletter says. The group claims to have chapters in Vietnamese communities around the world and a network inside Vietnam that extends into the north.

In the newsletter's first issue, the front claimed that its forces in Phu Khanh Province killed three Vietnamese soldiers and wounded another in a "brief clash" in February.

The newsletter lists the front's president as Hoang Co Minh, a former admiral in the South Vietnamese navy, and the commander of its "Armed Resistance Forces" as Dang Quoc Hien, a former army major.

Vietnamese government officials say Minh was killed during an incursion into Laos in July 1987.

In a telephone interview from San Jose, the newsletter's editor, Tran Dieu Chan, insisted that Minh was "safe and sound and leading the resistance movement in Vietnam." She refused to say whether the 38 men now on trial are members of the National United Front but denied that the group receives help from Thailand or any other foreign country.

In Washington, a Thai Embassy spokesman said he had no information about the suspects or their group, but said support of such a group would "categorically" violate his government's policies. "We have no policy of promoting resistance within any of our neighboring, friendly governments, especially Vietnam," embassy First Secretary Pisan Manawapat said yesterday.

Hanoi generally dismisses the front's claims as exaggerated, but appears to take seriously the potential threat posed by armed rebels and remains wary of what it says continuing efforts by "reactionary" overseas Vietnamese and "foreign intelligence agencies" to foment "subversion" here.

Michael Morrow, a visiting American businessman who was arrested during an internal security crackdown in April, later said one of his interrogators told him that the CIA was behind the fall of communist governments in Eastern Europe and now was targeting Vietnam. Morrow said Vietnamese intelligence was convinced of a U.S. "We have no policy of promoting resistance within any of our neighboring, friendly governments, especially Vietnam."

-- Thai diplomat Pisan Manawapatare

plan to instigate increasing "contra-style military penetrations" and "create a Tiananmen in Vietnam," referring to the Beijing square where Chinese protesters demonstrated for greater democracy in the spring of 1989 before being routed by government troops.

While this may represent a hard-line view, the latest attempted incursion is seen as "very serious" and a "crime against national security," said Justice Minister Phan Hien. He declined to comment on whether Hanoi believes the group has received U.S. government support.

According to Lt. Col. Le Phuc Nguyen, who has reported on the rebels for the army newspaper Quan Doi Nhan Dan and interviewed many of the current defendants, 139 intruders have been killed and 114 captured inside Laos in three attempts to cross into Vietnam from Thailand since June 1986. In the biggest incursion in July 1987, he said, 68 rebels were killed and 67 others captured and later sentenced to prison terms of 10 years to life after a trial in Ho Chi Minh City, formerly Saigon.

The leader of the August 1989 expedition has been identified here as Dao Ba Ke, 38, a former South Vietnamese paratroop lieutenant who uses the nom de guerre Tran Quang Do. He spent five years in a reeducation camp after the 1975 Communist victory, then eked out a living for three years by working as a pedicab driver in the southern town of Can Tho before fleeing Vietnam by boat in 1983, Nguyen said. In June 1984, he said, Ke was recruited from a Thai refugee center by Minh and taken to a training camp in the jungles of Thailand's Ubon Province near the borders of Cambodia and Laos.

According to the army newspaper, the rebels were recruited from Vietnamese "boat people" stuck in Thai camps with no hope of resettlement in the United States or other countries. Many had been jobless before fleeing Vietnam, some were "alienated" former government soldiers or cadres, some were petty thieves, and others were former street urchins known by authorities as the "dust of life," the paper said. Most are in their twenties and the youngest is 19, it said.

The front's long-range plan, Quan Doi Nhan Dan said, was to build bases inside Vietnam, sabotage factories, bridges, dikes and other targets to damage the economy and launch a "total uprising" to overthrow the government by 1992.

In a series of articles in September, the paper quoted captured members of the group as saying that recruits received training in weapons, tactics, map-reading and communications. It said foreign intelligence agents, who were not further identified, helped Vietnamese leaders run the camp and controlled the distribution of weapons.