THE 164 LETTERS comprising this collection may not be, as the preface points out "brilliant specimens of epistolary style." They do, however, constitute precious documentation of the hard ideals and ever-darkening temperament of Eugene O'Neill, arguably the greatest dramatist America has yet produced. They were exchanged over a 30-year period by O'Neill and Kenneth Macgowan, the young theater critic who in the early 1920s joined forces with the playwright and scene designer Robert Edmond Jones to run the Experimental Theatre at the Provincetown Playhouse in New York.

The correspondence is largely one-sided, all but a handful of Macgowan's letters having been lost to time. There is no question, though, that Macgowan served as a critical sounding board and trusted friend to O'Neill, a difficult and stubborn man who permitted himself few confidants. Reviewing a production of Beyond the Horizon, Macgowan sensed in the playwright an "incorruptible" genius and predicted "a man like that will write big plays." Opening the correspondence in February 1920, he invited O'Neill to attend the annual dinner of the New York Drama League. The invitation went unaccepted, but the ice was broken. Soon both men discovered they were fired by a common vision of an Art Theater. Most of the early letters, meticulously footnoted, deal with the particulars of bringing that theater into being--the endless minutiae of play selection, casting, fund-raising and royalties. (Throughout his life, O'Neill displayed a miser's preoccupation with money.) What knits these letters together, however, is the playwright's obsession with his own creativity, a deep and dark compulsion he obeyed often at the expense of his health.

At times, it seems, he couldn't get the plays in his head down on paper fast enough. When the juices momentarily dried up, he was pitched into depression. "I'm too low for the energy of ink," he writes, apologizing for a letter undertaken in pencil. Months later, he is crowing (of The Hairy Ape), "I was so full of it it just oozed out of every pore." From Bermuda, where he thrashes out The Great God Brown, he quips, "Come on, you 'Brown'! Daddy needs a yacht!' Soon after: "I envy those simple souls to whom life is always either this or that. It's this and that, the this- that desire . . . that slow-poisons the soul with complicated contradictions." That awareness of the ambiguity implicit in human emotions could make his life hell. It also made for theatrical masterpieces.

The working relationship between Macgowan and O'Neill ended in 1926 with the production of The Great God Brown. O'Neill then turned to the Theatre Guild to produce his plays, and Macgowan eventually forsook the theater entirely for motion pictures in Hollywood. Stripped of the immediate concerns of running a playhouse, the correspondence gains in intimacy and offers some rare glimpses into O'Neill's personal life. Shedding his second wife, Agnes, the playwright took up with the actress Carlotta Monterey, who would become his lover, wife, nurse, mother, inspiration and tormentor, all in one. (From the Basque country in France, where the two fled to avoid unpleasant publicity, he boasts, "Carlotta is a brick!") The subsequent letters and their far- flung postmarks bear witness to the O'Neills' feverish attempts to find a sanctuary, usually near the sea, that offered him the grand solitude necessary for his writing.

By 1940, O'Neill had all but given up the notion of seeing his ambitious plays staged in a manner befitting them. "The memory of the old P.P. (Provincetown Playhouse) days . . . moved me to a sad nostalgia," he informs Macgowan in November of that year. "There was a theatre then in which I knew I belonged, one of guts and idealism. Now I feel out of the theatre. I dread the idea of production because I know it will be done by people who have really only one standard left, that of Broadway success. I know beforehand that I will be constantly asked, as I have been asked before, to make stupid compromises for that end."

In his view, Broadway had become "a job, a business within the Showshop, a long, irritating, wearing, nervous, health-destroying ordeal, with no creative enthusiasm behind it," and he rails against "the Old Game, the game we used to defy in the P.P. but which it is impossible for me to defy now, except in my writing, because there is no longer a theatre of true integrity and courage and high purpose and enthusiasm. There are just groups, or individuals, who put on plays in New York commercial theatres. The idea of an Art Theatre is more remote now, I think, than it was way back in the first decade of this century." The indictment could have been penned yesterday.

The final entry from the O'Neills in this absorbing collection is dated December 6, 1950 and was actually written by Carlotta. The playwright, seriously afflicted with Parkinson's disease and prey to crippling bouts of pessimism, had taken refuge in a manse on the rocky shores of Gloucester, Massachusetts. "Gene is not too well," it notes, ominously. Three years later, he would be dead, having spent his formidable energies in the service of a theater so grandiose and probing that it could fully exist only in the tortured recesses of his own imagination.