After launching small boats into the South China Sea, sneaking into refugee camps in Thailand at night to avoid being turned back, and living for months in tents on snake-infested beaches, 37 Vietnamese refugees arrived at Dulles Airport Wednesday to begin new lives as American immigrants.

After tearful reunions with friends and family members who had escaped earlier, the refugees told stories of the harrowing escapes that have gained them special entrance into the United States as "boat cases." They are among 7,000 such refugees who began arriving in the United States this week.

Hua Ton, 36, a formerly wealthy chemical importer, said he smothered his infant niece unconscious to keep her from crying and giving away the escape of 63 fellow refugees.

Hua, like the other refugees at Dulles, said his life had become intolerable in Vietnam because he had become identified as a member of the old regime and a friend of the Americans.

"I was summoned for interrogation once and I was sure that soon I would be imprisoned in a re-education center," Hua said.

"Our family left Saigon for a distant province in small groups," he continued. "We disguised ourselves as peasants and bought a boat under the name of an islander. We waited 20 days for a chance to escape, when we thought the Communists were not watching."

Hua said he often feared he would die attempting to escape. His group spent "64 to 70" hours on the South China Sea before reaching a beach in Thailand. He and his family sneaked into the Leam Sing refuge center at night and set up camp, making it look as though they had been there for a while so they would not be evicted by guards.

"Conditions were bad: it was an extremely poor camp located in a cemetery. It was infested with all kinds of insects and snakes.We couldn't leave without permission and we were allowed only 5 liters of water (about 1 1/2 gallons) per person per day. Food was very bad and (small amounts were) provided only twice a week," Hua recalled.

"If you don't have money it's very hard to survive in a camp. We had to buy extra food and water. You have to buy everything," he said. Hua said he escaped with $10,000 in gold, $7,000 of which he spent supporting his large family in the camp. Among the possessions he left in Saigon were two warehouses and three cars.

Lam Thi My Phuong, 23, and her husband escaped last February aboard a small, rickety boat with a group of 31 friends and relatives, including their 2-week-old son and 2-year-old daughter.

They were met at the airport by her adoptive mother, Lam Thi Xanh, co-owner of La Fregate Restaurant, located on Florida Avenue NW. While the mother shook her head, clutched at her daughter's arms and said, "she's lost so much weight," Phuong and her husband talked about their escape.

According to Mrs. Xanh, who acted as interpreter for her daughter, the group spent about five days drifting at sea after the motor on their boat gave out. They left without food or money and were seasick much of the time. Like Hua's family, they arrived in Thailand at night and sneaked into a refugee camp. They bought food and water with $1,500 sent by her mother.

"I can't believe they're alive," exclaimed Mrs. Xanh, who tickled the grandson she was seeing for the first time. She said her son-in-law and daughter would begin working in her restaurant next week. "They're lucky, they don't have to apply for welfare," she said.

The Hua and Lam families are among a total of 15,000 refugees who will be admitted to the country under a new immigration program established to admit hardship cases. In addition to the 7,000 boat people, some 8,000 refugees who escaped overland to Thailand will be admitted.

Since the falls of Saigon 2 1/2 years ago, 150,000 Indochinese refugees have entered the United States. All but 15,000 came in a mass evacuation in the spring of 1975, and were not subject to traditional immigration quotas that limit entry to this country.

Congress authorized the admission of the additional 15,000 because their cases were so desperate. There are an estimated 80,000 refugees now living in camps alone, according to Richard Scott, Washington representative of the Intergovernmental Committee for European Migration, which coordinates travel arrangements for the refugee groups.

State Department officials estimate that 400 of 15,000 new refugees will settle in the Washington metro politan area, mostly in Northern Virginia, near their relatives.

Of the approximately 150,000 Indochinese refugees already living in the United States, 453 live in the District of Columbia, 2,001 live in Maryland, mostly in the Baltimore area, and 6,241 live in Virginia.

Officials say they expect that most of the newly arriving refugees - a group less wealthy and educated than the earlier arrivals - will have to accept such jobs as dishwashers, kitchen wokers and hotel maids where knowledge of English is not essential.

"We are willing to take any employment offered," said importer Hua. "We hate to be burdens on the American economy."

Federal funds for welfare assistance to refugees will run out on Sept. 30. Congress is considering several amendments to extend the program.

In a hearing on the proposals held yesterday before the Senate Committee on Human Resources. Under Secretary of State Philip Habib said it was likely that an additional 15,000 refugees a year would seek to enter the United Stateee over the next three or four years.