"Basically, I'm not tactful," confided William Goldman in the course of John Brady's invaluable book, "The Craft of the Screenwriter," a collection of six interviews with prominent movie dramatists published last year by Simon and Schuster. Goldman certainly confirms this prickly self-appraisal in the opening installment of the PBS mini-series "Screenwriters/Word Into Image," an intriguing but sketchy survey of the work and working problems of six movie dramatists which begins today at 10 p.m. on Channel 26.

Nervously adjusting a long, droopy mustache and barely keeping his voice from breaking the shrill barrier, Goldman shares some exasperated recollections, trade secrets and beefs (encompassed by the unifying complaint "nobody knows anything") with invisible, unheard interviewers -- presumably coproducers Frieda Lee Mock and Terry Sanders.

"Screenplays are structure, that's all they are," Goldman says in the wake of a clip from "Butch Cassidy & the Sundance Kid" -- the overused jumping-into-the-rapids scene.

Mock and Sanders have structured their half-hour portraits (with Goldman, Paul Mazursky, the late Eleanor Perry, Neil Simon, Carl Foreman and Robert Towne), around three or four excerpts, sometimes eloquent and sometimes not, from the subjects' backlog of screen credits, interspersed with first-person commentary meant to cover biographical and professional reflections.

The most flattering Goldman clip turns out to be the first suspicious newsroom encounter between Robert Redford and Dustin Hoffman in "All the President's Men." The producers also include some strenuous moments from "Marathon Man" that certainly can be said to originate with Goldman, since he wrote both the novel and screenplay, but seem to owe more to director, photographer and cutter for their sensationalistic impact in the finished film. When the selection process diverges from scenes that have little to do with character exploration or essential dramatic structuring, it seems fair to conclude that "Words Into Image" has misplaced the screenwriter's most important contributions -- and failed to pay sufficient attention to the first witness.

In fact, the half-hour format seems to lock each segment into an excessively repetitive structure and limited field of inquiry. The Foreman segment spends so much time on the allegorical aspects of "High Noon," intended by the writer as a camouflaged attack on Hollywood's reluctance to buck the House Un-American Activities Committee, that there's no time left for a word or two about his blacklisted work on "Bridge on the River Kwai" or his reemergence as writer-producer of "The Guns of Navarone."

One reason the series seems to compare so poorly to "The Craft of the Screenwriter" is that Brady, an astute and systematic interviewer, got there first with more extensive material. Three Brady subjects -- Goldman, Simon and Towne -- make appearances on "Word Into Image." The Simon installment wasn't available for preview, but Goldman and Towne clearly have more scope for reminiscence, advice and rumination in the printed interview.

Towne, probably the most subtle mind and talent interviewed, appears spacey and "Word Into Image" gives him an abbreviated, unflattering showcase only his dearest enemies could relish.

Apart from Paul Mazursky, whose background as an actor and status as a writer-director may give him more confidence as a camera subject, this series tends to remind you that writers are better off as words than as images.

One curious feature of the series is an attraction to profane dialogue and racy depiction that may prove difficult for many PBS outlets. Viewers can look forward to many explosive variations on the most famous four-letter word of them all on the Goldman, Mazursky and Towne installments, plus nude sunbathers in a clip from Mazursky's "Bob & Carol & Ted & Alice" and a Barbara Hershey striptease in a clip from the Frank and Eleanor Perry version of Evan Hunter's "Last Summer."

Eleanor Perry leaves the forlorn impression of having spent the last frustrating years of an initially overrated career hearing coarse expressions from producers and directors, supposedly indicative of the kind of earthy writing she was too sensitive to supply. She contributes a memorable self-pitying witticism--"On the misery graph of Hollywood, the writer's curve is the highest" -- and her own curve seems to go off the chart during this melancholy, posthumous appearance.