Arena Stage's production of "Ah, Wilderness!" is absolutely splendid Eugene O'Neill's only comedy will be playing through Jan. 7. and I doubt that you'll ever see it better performed.

To O'Neill his play was "a sort of wishing out loud, the way I would have liked my boyhood to have been."

The setting is that same Connecticut home he returned in Long Day's Journey into Night" in which he dramatized himself as he was six years after "Ah, Wilderness!"

He wrote it while creating a serious drama, "Days Without End," In 1932. Putting that aside for a week of rest, he conceived "story, characters, pilot scheme and practically all the details for the comedy in which George M. Cohan would star in the fall of '33.

It is a play of sunshine, beautifully realized in the setting of Robert Yodice and the lighting of Hugh Lester.

On the Fourth of July, 1906, the family of newspaper publisher Nat Miller is celebrating with traditional good will. Son Arthur is home from Yale, 17-year-old Richard has been discovering Literature and the younger Mildred and Tommy embody everyone's brother Sid is visiting and so is Nat's sister, Lily, who refused to marry Sid 16 years ago because he drank and he still does.

The play, then, affords some rich roles, and Edward Cornell, making his bow as an Arena director, has allowed the players admirable freedom. Two are especially interesting for after many roles with the company both have lately been coming into finely matured power.

Halo Wines, recently so fine in "Tales from the Vienna Woods," is Lily, a spinster schoolteacher who fears what would happen should she marry Sid, who alwasy swears he's going on the wagon and just as often winds up soused.

There is a moment when her sister-in-law urges Lily to take on Sid anyway. "Don't feel sorry for me," says Lily. Wines steps a couple of paces backward when she says that and the movement becomes a striking comment on the character.

This is but one of many details Wines has stitched into her characterizator another occurs when, at the dinner table, she conveys how Sid's behavior has dried her mouth. As she sips some water, you feel her relief. There is humor but above all heart-break in this moving portrait.

as good is Mark Hammer as bibulous Sid, playing his drunk scene with that cloudiness of mind which, to the plastered one, always seems blinding clarity. The line are swell, but Hammer's timing and understatement form a gem of characterization.

Another kind of acting achievement is James Jenner's as Richard. He is clearly well past 17, and for a time the character takes on an unintended dimension. Richard seems faintly retarded, But Jenner is skilled at craft and in time I accepted his performance for the techniques employed.

Robert Prosky, as the father, is masterful, and there was extra pleasure at the opening in watching him act with his young son, Andrew Land Proskym, as Nat's youngest, a role Andrew alternates with Michael Gates.*tBarbara Sohmers Essie is beautifully drawn, and there is good work from Annlce Jefferies as the prostitute Richard picks up in a bar.

Finally there are the costumes by Marjorie Slaiman, the period evoked through detailed understatement, with hairstyles for Sohmers and Wines a refinementworth noting. Everything about this production is strickingly well thought out and achieved. CAPTION: Picture, James Jenner and Annalee Jefferies, by Larry Morris-The Washington Post