IDIOT'S DELIGHT by Robert Sherwood; directed by Edward Cornell; setting by Tony Straiges; costumes by Mariorie Slaiman; lighting by William Mintzer; technical director, Henry R. Gorfein; production coordinator, Nancy Quinn. With Robert Prosky; John Wylie; Halo Wines; Stanley Anderson; Joe Palmieri, Richard Bauer; and Frank Muller. At Arena Stage through June 24.

How tempting it must have seemed, after a few weeks of rehearsals for Robert Sherwood's 'Idiot's Delight," just to quietly drop the play from Arena Stage's '78-'79 schedule.

Surely once the players fully understood what they were getting themselves into, some perfectly plausible excuse could have been found - a virus, a parking lot attendant's strike, a highly localized earthquake. Something.

But no.With all these possible outs available to them, the company plunged ahead, body, soul and budget. And last night they delivered a commendably earnest, energetic and elegant performance of what may be the most tedious piece of claptrap ever to win a Pulitzer Prize.

For three hours, a cast of 28 plus untold numbers of support troops strove to pump some life into this flaccid period-piece - and failed utterly.

Perhaps the two leads, Robert Prosky and Halo Wines, could have uncovered more depth in their characers and seemed more compelling as a couple. But otherwise the company earned awards for valor right down the line; and the playwright, posthumously, earned a gentle tweak on the nose.

He can afford it. Even if the Pulitzer committee were to revoke his prize at this late date, Sherwood would be left with three others - for the plays "Abe Lincoln in Illinois" and "There Shall Be No Night" and for his marvelous New Deal Memoir, "Roosevelt and Hopkins."

Many a socially aware author has, in his time, decided to sum up the state of western civilization in a cloistered allegory. Benard Shaw gave us "Hert-break House"; Philip Barry, "Hotel Universe"; and George Orwell, "Animal Farm." But this is a trap from which lesser talents have rarely come back alive.

For this attempt at the genre, Sherwood chose, as others had before and have since, a hotel setting - a fancy but regrettably guest-starved hotel high in the Italian Alps with views of Switzerland, Austria and Bavaria. Among the guests he registered at his hotel: an American showman (and his dancing girls); a German scientist; a Marxist (with no nationality); an international munitions mogul; a romatic, politically blind pair of English honeymooners; and a Russian woman of obscure origins and still more obscure purpose.

Into the mouths of these ciphers, Sherwood put lines like: "We've been trying hard not to know anything or to give a damn, but it isn't easy (the native young Englishman). And "Why should I go on saving people who don't want to be saved?" (the German doctor, as he resolves to turn his efforts from curing cancer to the service of his state). And "Who are the greater criminals? Those who sell the instruments of death, or those who buy them and use them?" (the munitions mogul).

The playhs appeal in 1936 sprang from a fragile composite of causes that could probably never again be recreated. The creed of pacifism (to which Sherwood had adhered) was just beginning to be put to the sternest intellectual test it would face in a century. That gave audiences the feeling that this was weighty stuff they were witnessing. And since they were also witnessing Alfred Lunt as the showman and Lynn Fontanne as the Russian, the experience must have had its light side, too.

Arena director Edward Cornell has written an admirable program note that praises Sherwood and his play for their 'simple heart beneath the worldly polish." And he has staged it with equal devotion to both.

On the heart front, Stanley Anderson (cast far more fortuitously than as Moliere's "Don Juan" his last time out) plays the Marxist with unbounded conviction, and Richard Bauer gives a controlled and touching performance as an Italian officer. Neither actor can make you forget what utter stereo-types their characters have become - but the stereotypes are vivid ones.

As for polish, Tony Straiges' state of-the-art deco set is a wonderfully wistful vision an age. Too bad they could not have come up with a play to match.