JOSEPH Papp was the foremost American theatrical impresario of our time - a major figure in the world of the performing arts. Operating from an institutional base - his New York Shakespeare Festival Public Theater - Papp brought live performances to a generation of playgoers, many of whom could thank him for initiation into its pleasures.Papp's seasons of free Shakespeare in Central Park would alone have been enough to reserve the Brooklyn-born producer a place in the pantheon of great promoters and presenters. As a nurturer of talent, he advanced the careers of numerous writers and performers who themselves have come to play significant roles in American theater. The list of writers would include David Rabe, Ed Bullins, David Henry Hwang, Ntozake Shange, David Mamet, Tina Howe, and John Guare, to name a few. Kevin Kline, Meryl Streep, M andy Patinkin, Martin Sheen, and Raul Julia - all of whom paid affectionate tributes at Papp's funeral Nov. 1 - typified the debt of the acting profession to the Public Theater and its founder. What became the six-theater complex on Lafayette Street in 1966 began modestly but boldly - with Shakespeare in 1954. Theater-within-a-church, theater in a small city park, theater on a flatbed truck marked the earliest stages of Papp playmaking. Later on, he would lock horns with another epic dreamer, Parks Commissioner Robert Moses. This was in 1959, when the festival was bent on ensuring its place as a permanent part of the Central Park scene. Moses insisted that admission should be charged, if for no other reason than to offset the expense of preserving the condition of the park site. Losing the first round, Papp won in the New York Appellate Court. Free summer Shakespeare has continued ever since, in addition to revivals on Lafayette Street. There the Public Theater is in the midst of Papp's bold undertaking - a Shakespeare Marathon of all 36 of the Bard's plays. The current production, No. 19, is "Pericles, Prince of Tyre." Papp's career was not a history of uninterrupted triumph. In 1973, he added the Lincoln Center Theater to his responsibilities. Notwithstanding several successes, audience response was disappointing. The association ended with Papp's resignation in 1977, partly because of his impatience with institutional restrictions. For the remainder of a career that ended with his recent retirement, Papp headquartered at the Public Theater. But the assorted spaces on Lafayette Street were insufficient to contain all the playmaking of the Papp vision. "A Chorus Line," which opened at the Public in 1975, subsequently moved uptown and became the longest-running show in Broadway history. The Public also had commercial successes with "Hair,The Pirates of Penzance," the Tony Award-winning "Mystery of Edwin Drood," David Hare's "Plenty," and Reinaldo Povod's "Cuba and His Teddy Bear." Pulitzer prizes were awarded to Charles Gordone's "No Place to Be Somebody," Jason Miller's "That Championship Season," and "A Chorus Line." There were also more than 20 Tony Awards. In 1972, the Public Theater won Tonys for both Best Play (David Rabe's "Sticks and Bones") and Best Musical (John Guare, Mel Shapiro, and Galt MacDermot's version of "Two Gentlemen of Verona"). Under Papp's leadership, and with a sometimes changing team of excellent professionals, the New York Shakespeare Festival has pressed forward in its role as its country's premier institutional theater. It has more than fulfilled Emerson's definition of an institution as "the lengthened shadow of a man." It continues as a monument to Joseph Papp.