Boston — They are heartwarming stories - the kind that show the United States can indeed still be a land of opportunity for those who work hard. In Pensacola, Fla.; in Chattanooga, Tenn.; and most recently in Boston, the spotlight at high school graduation exercises this spring has fallen on three young people with something in common besides their academic achievements.
All three fled a war-torn homeland in the mid-to-late 1970s. All arrived in the US speaking no English. Yet all graduated as valedictorians, the top scholars of their class of 1983.
All three are Vietnamese.
Moreover, all three plan careers in technical fields. Ironically, their performances stand out in contrast to recent criticism of a ''rising tide of mediocrity'' in US public education by a bipartisan federal commission.
The first to achieve the honor was Dung Nguyen, whom President Reagan phoned to congratulate on her graduation from Pensacola High School May 31. Miss Nguyen has been awarded a scholarship to attend Baylor University in Waco, Texas, next fall to study medicine. She reportedly plans to spend the summer selling encyclopedias in Louisiana.
On June 5 in Chattanooga, Hieu Pham delivered the valedictory address at Red Bank High School, telling his fellow graduates: ''We must keep in mind that nothing is free in this world. . . . We must work, work, work for the things we want.''
The young man, who also hopes to study medicine or computer science, escaped with his family in a fishing boat in 1975 as South Vietnam was falling to North Vietnamese forces.
Here in Boston on graduation day, June 6, Hoan Binh La stood proudly on the stage of the city auditorium in gown and mortarboard, facing the classmates with whom she had attended Madison Park High School for the past three years. ''Nothing is so difficult that we cannot face it,'' she said.
Miss Hoan, who left Vietnam at age 14 without her family, spent nearly a year in a Malaysia refugee camp, eating only coconut and food scraps and bathing in the ocean. Her parents, both factory workers, had saved enough money to buy passage out of Vietnam for one of their eight children. She eventually reached the US by ship, settling first in Monterey, Calif., before coming to Boston. Of the three valedictorians, she has lived in the US the shortest time.
Miss Hoan lives with relatives and earns money by working in a grocery store and tutoring other Asian children in English.
She plans to study computer science at Boston College, where she has won a scholarship. In high school she earned an ''A'' in every course, including advanced physics and trigonometry.
According to US Immigration and Naturalization Service statistics, more than 600,000 Vietnamese now live in the US. Their lives here have not always been easy. Even as Miss Hoan was graduating from Madison Park, vandalism and assaults in Boston against Vietnamese and others of Southeast Asian origin were on an 18 -month rise, police say. Texas, California, and other states have seen similar incidents.
Old antagonisms left over from the Vietnam war have turned refugees against each other in some cases, further complicating the acclimation to a new culture.
Still, says Darrel Montero, an Arizona State University specialist in the study of Vietnamese-Americans and author of a recent book on the subject, they have demonstrated ''an incredible tenacity'' that is typical of Asians who migrate to the US.
By 1979, only four years after the war, more than 250 support groups had been organized in the US by Vietnamese to assist other Vietnamese refugees, Dr. Montero says.
''I think we'll see more'' Vietnamese achieving high academic rank in the US, he says, just as Japanese and Chinese immigrants did before them.
''When you transplant someone, making it in the United States is so incredibly easy, compared with what they experienced in their own countries; whereas Americans take so much for granted,'' Dr. Montero says. ''In the long run, I think what we're going to see is the Vietnamese providing an excellent role model for [other] Americans to follow in school and in the workplace.''