Ulysses S. Grant, Robert E. Lee, George S. Patton Jr., Douglas MacArthur, Dwight D. Eisenhower . . . and now, Hung Vu and Jean Nguyen.

Ten years after the fall of Saigon and 12 years after the U.S. withdrawal from the war in Southeast Asia, two 21-year-old Vietnamese refugees joined the "Long Gray Line" of West Point graduates trained to lead American troops since 1802.

Under a cloudless sky high on this famous promontory above the Hudson River, Nguyen, daughter of a former Vietnamese army colonel, and Vu, son of a disabled Vietnamese air force officer, joined 1,008 other cadets today waving their diplomas and tossing their white caps high in the traditional salute.

Commissioned as second lieutenants, they are among the first three Vietnamese-born officers to emerge from the U.S. military academy. Phong Nguyen of Hayward, Calif., (no relation to Jean) graduated from the U.S. Naval Academy today. More than a score of Vietnamese refugees are enrolled here, at the Naval Academy and at the U.S. Air Force Academy.

"It is my duty to serve this country," said Vu, a slender youth with a serious demeanor. "So many Americans lost their lives in Vietnam. I see it as my duty to repay that debt."

In their gray swallow-tailed uniforms, maroon-sashed and brass-buttoned, in their white trousers, white gloves and spit-shined shoes, sabers at their sides, Vu and Nguyen marched onto the platform in the academy's astro-turfed stadium to receive their diplomas.

Nelson, Newsome, Nguyen, Nielsen, Nikoncuk, Nixon, Nolan . . . . No special shouts went up when the name of the first Vietnamese woman West Pointer was read over the loudspeaker. Such cheers were reserved for big athletes and for the class "goat," the graduate with the lowest grade-point average.

Flanked by two hulking classmates, the 5-foot-3, 115-pound Nguyen could hardly be distinguished in the Long Gray Line until, walking off the platform, she fairly hopped with joy down a gauntlet of classmates waiting in line, flashed an open-mouthed grin, and waved her diploma toward her parents and her five brothers and sisters in the far-away bleachers.

"I feel great, that's the only thing I could say," Nguyen told reporters. As for any symbolism about a Vietnamese at West Point, she said, "I don't consider myself the first this or that. I don't want to be singled out. I just want to be part of the class of '85."

The glory of this picture-patriotic day had not come without years of anguish. Vu remembers hiding under his family's sofa when Saigon was shelled during the 1968 Tet offensive.

"I could hear the bombs," he said in an interview. "I was scared. I cried."

Nguyen saw her father, Minh Van Nguyen, commander of the 6th Paratrooper Battalion, wounded four times and nearly killed. When the South Vietnamese Army surrendered, Jean Nguyen remembers, her father called his wife and children into his bedroom and, holding a grenade in his hand, said, "If we're going to die, we're going to die together, all at once. I will pull this trigger rather than let the communists take us away."

But both families were able to escape within days of Saigon's fall in 1975. Neither youth spoke any English when they arrived, Nguyen's family settling in Milton, Pa., under sponsorship of a Lutheran church, Vu's landing in Queens under the wing of the Catholic Relief Services.

"I was depressed," Vu said. "I tried to learn English by watching television. I didn't know what my future would be. At junior high school they called me "chink."

His father worked two jobs, at the Catholic Relief Services as a claims analyst by day, at the United Nations as a security guard by night. His mother took English at night school and now works as a hotel laundress.

Now the family, which came here with no money, has bought a $125,000 condominium in Queens, immaculately furnished and equipped with a microwave oven and a videocassette recorder. Now Vu listens to The Police, U-2 and other New Wave bands, goes dancing at the Peppermint Lounge and owns a new Honda Accord.

"It's the American dream," he said, and somehow it doesn't sound like a cliche.

Nguyen, who decided to apply to West Point despite her family's initial skepticism, said during her four years here she had to struggle academically. "Everything was difficult for me," she said.

But she added, "It taught me not to give up easily . . . . As a citizen, I felt I should do something for the U.S., my adopted country. I'm very glad to have the opportunity to serve in the Long Gray Line. "

"She grew up in a combat zone," said Col. Herbert Lloyd, a friend of the family since he served as a U.S. adviser to her father's battalion in 1963. "She had a steel will and determination. Vietnamese women have always been expected to stay in the background. She had to break a major cultural barrier."

Nguyen was praised by President Reagan in his recent State of the Union message and was brought to Washington to meet the president.

In the lobby of Grand Hall today, Vu's grandfather, Pham Van Tong, a retired furniture salesman who flew from Paris for the occasion, posed for a picture in his grey fedora, black patent-leather shoes and white socks before a life-size oil portrait of Eisenhower.

He beamed and, speaking French in a tone of wonder and glee, said, "This is serious. This is very, very serious.