Tammy Grimes is one of the few Broadway stars to have received Tony Awards in two categories -- for best Musical Comedy Actress in _The Unsinkable Molly Brown_ (1961), and for Best Dramatic Actress in Noel Coward's _Private Lives_ (1969). In a sense, she is Molly Brown personified -- a powerful stage presence whose charm, beauty, and pure talent make her shine in every production she takes part in, regardless of the overall merit of the show itself. Her disappointments have been, at times, as spectacular as her triumphs. For example, there was her shot at network television in the early 1960s, _The Tammy Grimes Show_, which lasted only 11 episodes because, she says, "the writing, the concept, and the talent never really got together. And I blame myself for that. Because if your name's up there, you are responsible for the product." Her marriage to actor Christopher Plummer ended in divorce after four years, but had the happy result of producing a daughter, Amanda Plummer, who is now a successful actress herself. Tammy played Molly Brown on Broadway for the show's entire two-year run, but the movie role went to Debbie Reynolds. She got some rave reviews for her acting in a Broadway thriller named _Trick_ this year, but the show closed within weeks. When that happened, she quickly started working on a new show, _Father's Day_ by Oliver Hailey, that is scheduled to open on June 21 at the American Place Theatre on West 46th Street. "It's about three women who get together on Father's Day," says Miss Grimes in an interview at her Upper East Side apartment. "They live in the same building, and they're divorced. It shows how the three of them are coping with the situation. My feeling is that they don't want to be divorced. It's a very well-written play -- a comedy. ... It's at the same theatre where _In Cold Storage_ started." The interview takes place in her softly decorated bedroom looking out on a garden. Tammy is propped up on pillows beneath the covers, smoking a cigarette and sipping a bottle of Tab as she apologizes for her condition. "It may have been the caviar I had last night," she says, cheerful in spite of her discomfort. Her pixyish features expand easily into a grin, and at 45 she has lost none of the childlike playfulness that first propelled her to stardom. But the most surprising quality about Tammy Grimes is her throaty British accent. Although she has done little work in England, her normal speaking voice is far more British than American -- a fact which, for some reason, she strenuously denies. "I spent a lot of time doing British comedy," she explains, "but I don't sound British!"