One day when he was 8 years old, Chris Thomas discovered he could talk just like Donald Duck and, with a little practive, mimic his teacher. Before long he was imitating John Wayne's prairie drawl. And by the time he was delivering the morning announcements over the public address system at Beltsville's High Point Senior High School a few years ago, he was reading each one in a different voice. You couldn't be sure if it was Thomas talking or the ghosts of Boris Karloff and Peter Lorre.

Today 19-year-old Thomas is an accomplished impressionist who recently talked his way onto stage at Constitution Hall, brought down the house and may be on his way to fame and fortune.

"I thought he would go over well, but he didn't just go over well, he went over super well," says Bill Washington, a concert-promoter who, on the spur of the moment, let Thomas take the stage before the headline act at a Constitution Hall concert three weeks ago. By the time Thomas had finished his routine -- which includes impressions of Howard Cosell, Wolfman Jack, Hubert Humphrey, Muhammad Ali, Sugar Ray Leonard and others -- he'd received a standing ovation.

Now Washington, president of Dimensions Unlimited, says he wants to use Thomas in the future -- for a fee, of course -- which may be the break Thomas needs. A second year-business student at Strayer College, Thomas is managed by two friends, the editor of Strayer's newspaper and the president of the student body. They formed a management company called Peter Rabbit Promotions.

For a couple of years now, since he started performing at local beauty pageants, Thomas had craved the bright lights. He's won audiences at New York's improvisational club, Catch a Rising Star, and at one of Washington's outlets for beginning comedians, Garvin's. Last year he traveled to Los Angeles to perform at The Comedy Store; he says he was asked to return each week but that he couldn't afford to live in California until he got rich.

"I do basically white voices," says Thomas, who thinks audiences are more impressed that a black man has mastered Jimmy Carter's voice than, say, Bill Cosby's. For local radio commercials, Thomas has imitated Ali, Carter, Paul Lynde and George Burns. He can switch voices easily, carrying on an imaginary but entirely believable conversation between Cosell and Ali while drawing from a repetoire that includes Bob Hope, Tom Jones, Orson Welles and more than 100 other voices. His latest project is the mastering of Ronald Reagan's voice -- just in case Las Vegas or Johnny Carson should call tomorrow.