"You can tell from mail that you do help people, whether you mean to or not," says the actress with obvious satisfaction. "I've gotten letters saying, 'Seeing Rita through that difficulty has enlightened me about my own situation.' She has not helped by example, because Rita doesn't always do things right. But she shows how much trouble you can get into by behaving the way she does, and in that way I think she helps people avoid the same mistakes." ******** EASTSIDER BRIAN KEITH Back on Broadway after 27 years 12-29-79 On January 1, 1980, the curtain will finally ring down on _Da_, Hugh Leonard's strikingly original and poignant drama about a man's fond memories of his working-class Irish father. _Da_ won four Tony Awards in 1978, including Best Play. Since July 30, the title role has been ably filled by Brian Keith, an actor perhaps best known for playing "Uncle Bill" in the situation comedy _Family Affair_, one of television's most popular shows from 1966 to 1971. Recently he has been seen in the TV specials _Centennial, The Chisholms_ and _The Seekers_. In his long, illustrious career, the 57-year-old actor has starred in four other TV series and appeared in more than 60 motion pictures. During the late 1940s, when he worked primarily on Broadway, Keith rented an apartment on East 66th Street with a fireplace and kitchen for $70 a month. Leaving for Hollywood in 1952, he eventually married a Hawaiian actress, and nine years ago became a full-time resident of Hawaii. "I hadn't been to New York for years and years and years, and when we came here for a vacation last winter, I saw a play every night for a couple of weeks," says Keith. "_Da_ was the only one I thought I'd really like to do sometime." Not long afterward, Barnard Hughes, the Tony Award winning star of _Da_, decided to tour with the show, and Keith was offered a five-month contract to replace him. Delighted with the chance to return to Broadway in such a compelling role after a 27-year absence, Keith quickly said yes. Bringing his wife and children to New York for an extended visit, he again chose the Upper East Side as a place to live. A big, brawny 6-footer whose deep, gravelly voice and slothful mannerisms somehow bring to mind a friendly trained bear, Keith normally spends the time between his matinee and evening performances sleeping on an Army cot in his dressing room. On this particular day, he is sitting in the sparsely furnished room with his shirt off, smoking a cigarette and answering questions about his career. His initially gruff demeanor soon gives way to laughter, sentiment, hopefulness and cynicism in equal measure. A no-holds-barred conversationalist, he talks about the acting life with a rare frankness.