He has been called the country's most powerful novelist of the post-Vietnam era—a soft-spoken part-time college professor who illuminates the darkest corners of the American psyche with brilliant prose. His maiden effort, A Hall of Mirrors, won the Faulkner Award for the best first novel of 1967. Dog Soldiers earned him the prestigious National Book Award in 1975. With the publication of his third book, A Flag for Sunrise (Knopf, $13.95), Robert Stone, 44, has another literary prize in sight: He was nominated this month for the American Book Award, which has replaced the National. What's more, he may finally be attracting a wider popular audience. The author finds that both pleasing and unsettling. "I'm just not used to it," he says.

A Flag for Sunrise is the hard-edged, often violent story of four Americans who find themselves in an imaginary Central American country on the brink of revolution. Like Stone's other books, Sunrise tackles America's latest political obsession. "The situation down there reminds me of Vietnam," explains Stone. "We've been sending in Marines and pushing people around for a long time. Someday we'll pay for it." The idea for Sunrise came to Stone while he was traveling through Nicaragua, Honduras and Costa Rica in 1977. "In my younger days," he says, "I made it my business to be around wherever things were happening."

One such place was, of course, Vietnam. Stone spent three months there in 1971 as a correspondent for a now defunct British magazine, an experience that formed the background for Dog Soldiers. He visited combat zones on a motorcycle but spent most of his time in the war-torn capital. "I got to know more about the drug scene in Saigon than I wanted to," reports Stone. "Everyone was smoking heroin." Including Stone? "That stuff is illegal, isn't it?" he says with a smile. Stone's work has been criticized for his excessive emphasis on drugs and mayhem. He objects to the charge. "I've been around some pretty violent scenes," he admits, "but this is a pretty violent country. I'm concerned about it, but I think people should understand it too."

Born in Brooklyn, Stone was the only child of a dockworker. "My mother was schizoid," he says. "I spent three years in an orphanage." Kicked out of high school ("I'd show up drunk"), he joined the Navy, then bounced around from job to job until the first chapter of A Hall of Mirrors earned him a fellowship to the Stanford University creative writing program. In California he met novelist Ken Kesey, who was experimenting with drugs and running around with a group of social dropouts called the Merry Pranksters, later immortalized in Tom Wolfe's The Electric Kool-Aid Acid Test. "I still feel close to them," says Stone. "That was my gang, my college. It was like a big party that spilled out onto the street, then across the country. But by 1964 I wasn't getting any work done, so I came back to New York."

In 1969, two years after Mirrors was published, Stone packed up his wife, Janice, now a social worker, and their two young children and headed for London. From there Stone went to Vietnam. "When I got back to the U.S. in 1971," he recalls, "it was a different kind of country. With the war, the drug explosion, the music and all the wild things that were going on, it was almost like living in the aftermath of a revolution."

Today the Stones live with their daughter, Diedre, 21, in a small college town in Massachusetts. (A son, Ian, 18, is a college freshman in Wisconsin.) The novelist wants his exact whereabouts kept a secret. "I write about a lot of strange people," he reasons, "and I don't want them coming around to hassle me." He usually rises at dawn, makes a pot of tea, then sometimes works all day.

In the past Stone has traveled far afield to research his novels, but he plans to stay closer to home for the next one, a book about the effects of the Industrial Revolution on a small New England mill town. "It's hard not to think of yourself as young and indestructible," he says, "but my proper business now is writing. Besides, the people in my books are alternates for me—they go through all that horrendous stuff so I don't have to."