LABELING his play a 30-year-old project is misleading, says Austin Pendleton. The veteran stage, television, and film actor, and Tony-nominated director makes his playwriting debut with "Booth is Back," running through Nov. 3 at New Haven's Long Wharf Theatre. Mr. Pendleton first worked on the idea as a Yale undergraduate in 1960.The play is a sprawling saga of Shakespearean actor Junius Booth, who dominated the theatrical landscape of the United States in the early 1800s, crisscrossing the country with his acting troupe, and of his son Edwin, who went on to replace him during the second half of the century. "It's about a father and son who have not known each other," Mr. Pendleton explains, "who fall into a very dynamic, pressured relationship with each other, pushing them to places they would not have gone to otherwise, including the darkest parts of themselves." He is quick to add that what they undergo reflects "almost any relationship. That's what really close relationships are." (Although only seen in the play as a minor character, another of Junius's children, John Wilkes Booth, went on to gain infamy as President Lincoln's assassin.) The current version of "Booth is Back" reflects the intricate process serious plays undergo in their development. Initially called "Booth is Back in Town," it was a musical, and for years, various versions were tried. During the early 1980s, musicals such as "Gypsy" and "West Side Story" had successfully made their mark incorporating dramatic, even dark elements in their story lines. "But in both of those, they found something in the lives of the characters that lent itself to music, or to dance, which is not there in 'Booth.' We kept reworking it and reworking it, and finally it was done at the Pepsico Summer Festival in Purchase, N.Y., in 1983. It was a disaster," Pendleton says. He says he now realizes that "the script kept trying to get into the relationships, but also trying to fulfill the demands of being a musical. After that production, no one would even return our calls abou t it." Reluctantly, he put it aside. Last year, the idea again caught his imagination. "Along the way, some people told me it should be a play, and I would say no, no." But he decided to rethink the entire project. When the artistic director at Chicago's Steppenwolf Theatre Company, where Pendleton is a member, could not see the musical script as the basis for a play, "I realized there wasn't enough left of my original intentions for someone else to see." He dug out his college script and discovered the source of his original passion. He st arted over. "I completely re-researched it." A staged reading of his new draft in January revealed the new focus, and was strong enough to interest both the Williamstown (Mass.) Theatre Festival and the Long Wharf Theatre to include a production on their 1991 schedules. Long Wharf director Arvin Brown read the draft, and he "jumped on it that very day. Austin has one of the finest minds I know, but unlike many people like that, who tend to be only 'head people,' he is also in touch with feelings and emotions," Brown says. He sees it as "a big play, with themes beyond the central theme, wide in scope." Last August, the play received its workshop presentation at Williamstown. On its opening night, despite the fact that reduced rehearsal time required some actors to carry scripts, the audience was enthusiastic. From its reading in January, to that production, "the whole third act was completely reconceived." Throughout the Williamstown run, scenes were rewritten, introduced, or thrown out. "As an actor, you get a sense of what will play, what will ignite an actor, what will make a moment active," Pendleton says. Actor Raphael Sbarge's work in the role of Edwin has been one of the production's high points. "This is a very intense, emotional part, and one in which Edwin is on the receiving end for most of the story, and then explodes," Mr. Sbarge says. "It's a son's struggle to help his father, and define himself through his father." He listened to tapes of Edwin Booth's performances to unlock the actor's temperament and style. He points out that actors in the last century "were treated like gods," because they provided live entertainment for a growing country with a large appetite for entertainment. "Both Junius and Edwin were actors whose craft was to perform in a way that elevated life to a larger scale, allowing people to see themselves in the characters and stories," Sbarge says. The robust play has been eyed for a possible move to other locales, possibly Broadway, following earlier Long Wharf productions such as "Joe Egg,Long Day's Journey Into Night," and "All My Sons." Pendleton is realistic about the possibilities, however, knowing producers' reluctance to invest in drama, given the high costs. "There are plays that, if people actually went into the theater, they would like them, but it's hard to get them there," he says. For now, the Long Wharf run has been successful enough to warrant continued development. He is delighted that audiences have responded to the rich, textured story, something he says any serious play should aspire to do.