Analyzing the scheduled seasons of American resident theaters, this October's American Theatre magazine found that William Shakespeare is still the most produced playwright in the country. Writer John Istel, looking at 1985-86 seasons for 150 theaters, found that Shakespeare's comedies are being done more often than his tragedies; "As You Like It," for example, will be done at seven theaters; "Hamlet" at two.

Charles Dickens is also high on the list, thanks to the inevitable "Christmas Carols" being performed at at least 20 theaters. There is hope for relief, however -- Barbara Field, who wrote the most-used "Christmas Carol" adaptation, has produced one of "Great Expectations," which will be toured to 30 states by a group from the Guthrie Theatre.

Of the contemporary playwrights, Athol Fugard is the most popular this year, with 15 productions of his plays coming up, including one of "The Blood Knot" at the Yale Rep in which he will costar with Zakes Mokae. Sam Shepard, also known as Jessica Lange's boyfriend, is close on his heels, with 14 productions across the country. He will direct a new one, "Lie in the Mind," at the Mirror Repertory Co. in New York. "On the Verge or The Geography of Yearning," a little-known play by Eric Overmyer, is being produced a surprising seven times this season.

Four productions of Arthur Miller's "The Crucible" are planned. Chekhov's "The Cherry Orchard" will also get four productions, including one here at the Folger.

There are fewer big musicals this year (see below for news of one at Ford's Theatre), but the modest "Quilters," which flopped on Broadway last year, is getting seven productions in the hinterlands. "Pump Boys and Dinettes" will be done four times.

There are some new plays being done, such as Toni Morrison's first play, "Dreaming Emmett," which is about the Rev. Martin Luther King Jr. It is scheduled to go into production in January in Albany, N.Y. New Plays by A.R. Gurney and Harry Kondoleon are coming up at Playwrights Horizons in New York, and August Wilson will present his third new play in as many years at the Yale Rep.

Women playwrights are gaining ground, with productions of three Caryl Churchill plays, seven "Painting Churches" (Tina Howe), six of Marsha Norman's " 'night, Mother," including one opening next week at Arena, and six of Wendy Wasserstein's "Isn't It Romantic."

But the most frequently done play this year, the one done more often than anything by Shakespeare, Dickens, Shaw or Shepard, is -- the envelope, please -- "Greater Tuna"! Ten theaters are planning this two-character character parade, which has already played Washington twice.