THE EMERALD FOREST. DIARY. By John Boorman. Farrar Straus Giroux. 229 pp. $14.95.

INSIDE WARNER BROS. (1935-1951) Selected, edited and annotated by Rudy Behlmer Viking. 358 pp. $19.95.

TWO NEW BOOKS provide intimate views of the filmmaking process past, present and future amorphous.

Both are entertaining and informative -- surprisingly so in the case of Boorman's diary. It reveals the rational, well-intentioned and personally attractive aspects of a man whose movies, The Emerald Forest conspicuously included, tend to collapse under the burden of portentous and ill-conceived mysticism. While one perceives what it is in his myth-cherishing, wrongheaded makeup that compels Boorman to be the most maddening talented director in the English-speaking cinema, the voice that speaks directly hrough this account of a contemporary film's three-year gestation is also sincere, edifying and frequently witty.

For example, Boorman is aware of his own worst habits: "I am impatient with exposition; I plunge into the heart of scenes, confusing and alienating an audience that may need a little coaxing to climb on to the rollercoaster; I make characters too quirky and eccentric. My films are overwrought; I am led astray by cinematic effects, etc." The problem, it seems, is that he's the prisoner of an untrustworthy unconscious when on the set and commanding the cameras to roll. Boorman's analysis of the Hollywood power merry-go-round, on the other hand, cannot be faulted:

"Hollywood today functions and is run by a small group of people who are in adversary stances yet mostly interchangeable: eight or nine studio heads, another forty-odd executives, perhaps sixty top agents, a dozen influential lawyers, as many business managers, a ndred active producers. There are directors and stars with great power over their own pictures, but they do not influence the way the town is run.

"Most agents . . . have two escape routes, either become a studio excecutive, or an independent producer . . . When a studio head is looking for an executive, he inclines toward hiring an agent because (a) he was probably an agent himself, and (b) agents are the people he talks to every day. Effectively, agents weave a cocoon around the studios so that they can reach directors, writers, actors, only by way of the agencies. They all talk to each other all day on the telephone . . . People who actually make films are in another business. While they are off on location . . . the producers and agents and studio executives gossip away, wheeling and dealing, nervously watching the grosses of each new movie and constantly revising the unwritten lists of directors and stars who are 'in' and 'out.'"

It's a pity Boorman has never established such a straightforward tone in his work, so freighted with otherworldly longings that you doubt if a fantasist this wacky could have a commonsensical neuron in his cortex. But of course he must in order to get anything on film in the first place. The Emerald Forest Diary is a reassuring reminder that even guys who prefer to keep their heads in the clouds still know how to keep their feet on the ground.

RUDY BEHLMER has made an agreeable specialty of extracting documentary treasure from the files of the Hollywood studios in their late, lamented Golden Age. He was the editor and annotator of Memo From David O. Selznick in 1972 and America's Favorite Movies, an anthology of behind-the-scenes production histories, in 1982. In the latter he dipped into the Warner Bros. corporate files to recreate the circumstances that gave posterity entertainments as likable and durable as The Adventures of Robin Hood and Casablanca. His latest collection begins a bit earlier than the title indicates, with some correspondence from the middle 1920s (Ernst Lubitsch and the Brothers Warner reaching a parting of the ways), but the bulk of the documentation covers the studio's vintage years of the '30s and '40s, which the editor also affirms to be the most thoroughly documented years.

A diverting miscellaneous read for confirmed movie nuts, Inside Warner Bros. recommends itself as an ideal gift item for friends who want to know a little more about movies like Captain Blood, Jezebel, Robin Hood, The Roaring Twenties, The Sea Hawk, Knute Rockne -- All-American, The Letter, High Sierra, Kings Row, The Maltese Falcon, Now, Voyager, Yankee Doodle Dandy, Mildred Pierce, The Big Sleep, The Treasure of the Sierra Madre, The Fountainhead and A Streetcar Named Desire, plus the personalities embroiled in their creation and manufacture. Since most of the titles are also available on videocassette, generous gift- givers might cons packaging a Warner Bros. classic with a copy of Inside Warner Bros.

One of the more intriguing revelations: an exchange of letters indicating that Notre Dame effectively blackballed James Cagney, the studio's choice, from playing Knute Rockne, since the college administration had been highly offended by his support for Spanish Loyalist lobbying groups. And somewhere in France, aging auteurists may be heartbroken to encounter conclusive evidence that Hal B. Wallis, the studio's production supervisor, instructed many directors how to shoot their pictures. The most pathetic example is Raoul Walsh, the target of repeated Wallis missives to loosen up and visualize scenes in something other than static closeups. "Put the camera on a dolly and move it a little bit," he orders, after viewing rushes from The Strawberry Blonde. His parting instructions are almost poignantly elementary: "I wish you would think out ahead of time every sequence you go into from now on, and figure the best way in which to shoot it to get the most out of it in the way of business, camera angles, and everything else. Let's try to get some composition, and some moving shots, and some interesting stuff in the picture."

Not every director seemed a remedial case, of course. Even when suspicious of their methods, the Warner executives were willing to let directors like William Wyler, John Huston and Howard Hawks operate without intrusive supervision. But there was no reluctance in men like Wallis and Jack L. Warner to exercise the authority entrusted to them. In this respect Inside Warner Bros. will provide a fascinating contrast to Steven Bach's Final Cut, the definitive portrait of a modern film company (United Artists) in which executive authority ceased to exist.