When Vietnamese-born David Diep Thai, from Seattle, opened a coffee kiosk on the shore of Hoan Kiem Lake last year, he never imagined that one day he would be serving espresso to the United States' first ambassador to Hanoi.

Yet this afternoon, with "As Time Goes By" playing in the background, Thai chatted with Ambassador Douglas "Pete" Peterson about the major changes underway in Vietnam.

The occasion was all the more remarkable because of the personal histories of the two. Peterson is a former prisoner of war, and Thai was a South Vietnamese who left the country on one of the last American helicopters to fly out of Saigon, now Ho Chi Minh City, in April 1975. More than two decades later, both men have been welcomed back warmly by a country that once shunned and condemned them.

Although separated by a generation, Peterson, 61, and Thai, 24, are part of a new American presence in postwar Vietnam, where "VC" is now more likely to mean venture capitalist than Viet Cong.

Once measured in U.S. troop strength, the American presence in Vietnam is now gauged by the number of corporate foot soldiers and franchises descending on one of the world's last communist countries.

Peterson, who arrived in Hanoi on Friday, strolled about the city today. Across the street from Thai's Au Lac kiosk is Connecticut-based Carvel ice cream. Baskin-Robbins is here and expanding. TGI Friday and Kentucky Fried Chicken are scheduled to open their first outlets in Ho Chi Minh City next year. And McDonald's is reportedly on the way. Thai will soon be selling fried chicken at a place he plans to open called Cock-a-doodle-doo.

Although the United States ranks ninth on Vietnam's list of top investors, the American influence here is dramatic, at least on the surface.

Thai, who plans to market his fried chicken primarily to the Vietnamese market rather than to expatriates, predicted success, in part because the food will be served fast and "the price will fit their pocketbooks."

Susan Gajete, manager of the American Club, an expatriate hangout on the site of the former U.S. consulate here, disagrees that Vietnamese tastes as so malleable. "You give Vietnamese kids cheeseburgers but they still want pho," a popular noodle soup, she said. "You give them hot dogs, but they still want rice."

However, Thai said he is confident because he has had a hand in shaping the market's tastes. Thai is a Viet Kieu, or one of the 2 million Vietnamese who fled overseas after the war. About 1 million settled in the United States, where they adopted American tastes that they then introduced to Vietnam.

"A cultural osmosis takes place in Vietnam when Viet Kieu come back, because they are always talking about America this or America that," said Thai, whose family used to send packages back to Vietnam containing items from shoes to music videos.

Deac J. Jones, who imports American goods to Ho Chi Minh City, said the Viet Kieu have been more influential in shaping local tastes than the infusion of young Americans during the war years. "Some people remember American icons like Campbell's soup from before the war," he said, "but half the population is under 20, so it doesn't matter with them."

"Everyone loves Cindy Crawford," said Hoang Thi Thu, 21, a Revlon salesclerk who sells as much as $300 worth of cosmetics a day at the Superbowl, a Ho Chi Minh City shopping mall -- not bad business in a country where the per capita income is just $300 a year.

Ice skating until 4 a.m. has become the newest sensation in Ho Chi Minh City, and dance clubs are full of young people wearing American designer-label clothes. The American allure extends to unauthorized, copycat versions of well-known restaurants such as Spago, Planet Hollywood (called Planet Saigon) and the Hard Rock Cafe.

And here in Hanoi, a Vietnamese university class on American culture uses films such as "Good Morning, Vietnam" and "Pulp Fiction" as teaching aids.

With so much of Vietnam's youth focused on American-style flash and consumerism, the old guard has begun complaining about the loss of traditional values. Newspaper and television editorials criticize the corrupting influences of Western consumerism, loose morals and the rising use of heroin and other drugs among students.

"The government is moving along very cautiously because they fear social evils from the West," said a U.S. diplomat who requested anonymity. Other observers say the Vietnamese leadership fears the possible destabilizing effects of Western ideas and rapid social change.

"It's like the U.S. going from the 1930s to the 1980s in 10 years," said a lawyer from California who has lived in Vietnam for six years. "That's the kind of change we're talking about. The generation gap is exacerbated."

Pham Hoang Son, 25, manager of the popular Apocalypse Now bar here, said the very young are losing part of their heritage. "If you ask them about Vietnam's revolutionary heroes, 90 percent couldn't tell you," he said. But he added that nearly everyone remembers Ho Chi Minh because he's "worth remembering."

Even if the postwar generation -- children who grew up in peacetime and during the country's economic reforms -- are unaware of the historical details, most retain a strong national identity forged by centuries of Chinese and French colonialism, historians and other analysts say.

The government hopes that sense of identity will draw more overseas Vietnamese back to invest, despite lingering fears that anti-communist organizers might try to undermine the system. The Viet Kieus' skills, if not their capital, will help the country modernize, the thinking goes. Even their Americanization is considered an asset.

Thai, for example, uses corporate-speak like "synergy" to explain his success managing three businesses. He runs "smiling" workshops and customer-service role-playing for his staff. And he credits his success to a "can-do" American attitude.

"When my family first moved to the U.S., I grew up poor," said Thai, who as a child sold candy bars after school. "But America told me that I could create my own destiny if I worked hard enough."

He is working with a U.S. consulting firm to bring American and Vietnamese businesses together and dreams of creating a nonprofit academy to teach math and English to local street children.

"I'm glad I had the chance to tell the ambassador where I think Vietnam is headed," Thai said. CAPTION: A street vendor sells tea as Douglas "Pete" Peterson, the first U.S. ambassador to postwar Vietnam, walks with an entourage of officials and members of the news media beside Hanoi's Hoan Kiem Lake.