For about ten inmutes in the second act, a fine musical version of Juno and the Paycock is currently on view at the Shubert. These ten minutes show a backyard party, conducted to the tune of a cheerfully cheesy waltz, suddenly interrupted by the entrance of a woman on the way to the funeral of her son, who had been killed fighting for the Irish Republic. Most of the party, suddenly chastened, troop out as mourners, and the man who had been forced to inform on the dead soldier tries to relieve his feelings in a desperately gay dance.

The sudden, violent switch of emotional tone, the ironic play on the tension between gaiety and sorrow, are typical of O'Casey, and their effect is heightened by Marc Blitzstein's music and Anges de Mille's choreography. Tommy Rall does the informer's dance with what looks like incredible virtuosity. The incident is milked a little too heavily, but it works.

The remaining two hours of Juno are generally undistinguished, except for a refreshing lack of the sleaziness and greasiness which still stain most musicals. The major trouble is book trouble: Joseph Stein's script, with its long scenes of aimless small talk taken largely intact from the play, is a monument to misguided fidelity. Mr. Stein has already been chewed out by O'Casey's admirers for associating himself with a huge job of lily-gilding. It seems to me, on the contrary, that what Juno needs is fewer drab, limp petals, and more bright fresh gilt.

O'Casey derives his humor from bare-faced lying, brazen self-contradiction and other forms of impudence, chutzpah, and general damned cheek on the part of his characters. These are old theatrical devices; O'Casey handles them crudely, and Mr. Stein can think of no improvements.

But all is not cakes and ale in June nor even sausages and stout. There is supposed to be pathos, too, in the spectacle of poor, hard-working Juno Boyle slaving away to support her husband, a strutting "paycock" who spends his days carousing with his crony in the pub. But there isn't. The story of Juno's daughter, Mary, who impregnates and then deserts her, raises the possibility that O'Casey is the arrantest disher-up of unrefurbished cliche who ever presumed to deal in "serious" drama. Only in the account of Juno's son, Johnny, the unwilling informer, do O'Casey and his faithful amanuensis ever succeed in evoking sympathy.

Proceeding, perhaps, on the tenable theory that what they had in hand was a revival of O'Casey's play with occasional interpolated musical numbers, the producers engaged Melvyn Douglas and Shirley Booth to play Captain and Mrs. Boyle. Nothing in their performances compensates for their egregious violation of the rule that he who can't sing, shouldn't. Mr. Douglas at least does a good gruff job on what emerges as a thoroughly nasty character, but Miss Booth, in what should be a congenial role, seems almost uncomfortable; her famous infectious warm-heartedness is unaccountably missing, as well as her knack for pleasant semi-singing. Jack MacGrowran, as the Captain's fairweather sycophant, Joxer Daly, makes a pleasant if repetitive performance out of his slight build, weasly face, and nimble-stepping cringe. The other roles are taken mostly by singers and dancers whose acting appears to stem more from necessity than inclination.

The enjoyably folksy songs and dances are the best part of an evening that is, after never less than indifferent, and somehow never dull. Rumor has it that a new ballet will be inserted, and this sounds like a fine idea. If enough desultory backchat is cut out to make room for it, if director Vincent J. Donehue can do something about several performances, if the lyrics to more of the songs become audible, if a great deal of miscellaneous tinkering is successfully accomplished, Juno might be okay. But don't bet on it.