A Buddhist monk who had served the last two years as the liaison between the Unified Buddhist Church of Vietnam and the Communist government there has fled his homeland to report on what he describes as a sharp curtailment of religious freedom in Vietnam.

The Venerable Thich Man Giac, 48, formerly a university professor and deputy rector of Van Hanh University in Saigon, is touring the United States to tell about imprisoned monks and priests, smashed religious statues, sacked pagodas and besiezed religious organizations in Vietnam.

In an interview at the Buddhist Congregational Church of America at 5333 16th St. NW, Giac said he believes Americans should be made aware of the situation in Vietnam.

"In Vietnam, they listen to the Voice of America and the BBC," Giac said through an interpreter, Cao Ngoc Phung, a Vietnamese woman accompanying him here. "When they (Vietnamese) hear Jimmy Carter speaking about human rights they say. 'Oh! He makes beautiful statements about human rights,'" the monk continued. "There is a new gem of hope."

After visiting the large Vietnamese community in Paris, Giac said he came here "to share our experiences with the good American people (who have many links with the people of Vietnam, bad links or good, but they have links, and we have to accept that."

With the aid of the Vietnamese Buddhist Peace Delegation in Paris, of which Cao Ngoc Phung is executive secretary, the monk put together a mimegraphed booklet documenting detailing alleged human rights violations.

Giac's charges of government curtailment of religious freedom range from government cadres building an outhouse "very close" to a temple to numerous accounts of arrests - including that the head of the Unified Buddhist Church, the Ven. Thich Quang Thanh, who was detained for three months. He also alleges a government cover-up of information about the immolation of 11 monks and 1 nun in November, 1975. The 12 took their own lives, Buddhists asserts, to protest the religious repression by the government.

Included in the booklet are photographs of historic religious statues reportedly smashed by government cadres and sacred pagodas that have been burned.

Giac maintains that when Communist forces took charge throughout Vietnam after the American pull-out, Buddhists made every effort to assure the new government of their cooperation.

"Having faith in the promises of national reconciliation made by the Provisional Revolutionary Government, (Buddhists in Vietnam) since the day of liberation have done their utmost to cooperate with the revolutionary government," said a statement by the executive council of the Unified Buddhist Church. The statement is in a booklet of documents the monk brought with him.

"We believe we can go along with a demanding program for social revolution . . . We want only to be Buddhist and socialist at the same time," the Buddhist leaders' statement said.

Buddhist leaders repeatedly were rebuffed when they attempted to discuss with the government the alleged infractions of religious freedom, Giac said here.

Last March, he said, the Buddhist Church sent the government a memorandum detailing 85 "cases of oppression" and requesting the government to investigate. The church received no reply, he said.

The genial, softspoken monk, who lost his teaching post at Ho Chi Minh (formerly Saigon) University when he refused the government's demand that he relinquish his religious vows, acknowledged that some churches and pagodas continue to exist as showcases for tourists and journalists.

"They don't want to wipe out all of them. Some of them continue as exhibits. They know everybody's eye is on Vietnam, and a number of reporters are brought to specific temples to show that we are free (to worship). But in the countryside, it is a different matter," he said.

The monk left Vietnam last summer when some Vietnamese, planning to flee in a small fishing boat, sought someone who could speak Japanese. "They had heard on the radio of some refugee boats being picked up by Japanese ships," said Giac, who had studied for six years in Tokyo.

Leaders of the Unified Buddhist Church decided Giac's escape would provide an opportunity to tell the world about Vietnam. They encouraged him to join the escapees.

"We were 79 people in a boat about 8-by-72 feet. There was not even room to lie down, and we were at sea for eight days," he said.

The escapee's landed in Malaya and, after a few weeks in refugee camps there, Giac went to Paris where Cao Ngoc Phung and others in the refugee community translated documents he had brought and arranged sppeches in Europe.

Giac was received in Europe much more warmly than here. "In Europe, we were welcome everywhere," said Cao Ngoc Phong who had taught biology at the University of Saigon before leaving Vietnam in 1969.

"Here, no one wants to hear us. We tried to make a press conference, but nobody came," she said. She paused before added in a tone of dogged desperation:

"But we must keep trying. If you don't do anything, you are killing the people in Vietnam."