Sophisticated comedy is hardly at home in Hitler's Europe. But it is there, amidst scenes of the suffering and misery that have unfolded since 1939, that MGM has placed its latest effort at well-bred laughs, "Once Upon A Honeymoon." The cast is sure-fire, Ginger Rogers as a Minsky Melter gone broad A, Cary Grant in a reporter part tailored to his tongue-in-cheek virility, and a newcomer, Walter Slezak, as the type of Brownshirted bully that gestapoes himself into disfavor handily. But even these stalwarts are helpless in a plot that ambles from fantastic nonsense to the borders of poor taste.

The nonsense concerns Grant's rather natural interest in the little ecdysiast gone good via marriage to one of Der Fuehrer's greasier agents. Fifth-columnist Slezak and bride tour Europe on a sort of official honeymoon, with newshawk Cary watchfully in tow. In no time at all countries begin to fall, and with them the plausibility of the film. What had been witty dialogue now falls flat, what started out to be a whirlwind plot is slowed by refugees and the agonies of captive peoples. Director McCarey makes no attempt to eliminate the more sordid elements from the story, and the resulting hodge-podge swings from laughter to laments with unnerving rapidity.

Cocktail parties in Warsaw miss their mark when a Jewish family is about to be "liquidated." Dialogue in a Polish concentration camp is smothered by the wails of an entire colony on its way to the Nazi form of final justice. A honeymoon through northern France loses its gayety when interrupted by streams of panic-stricken refugees.

It would take a master to mold these diverse elements into a cohesive story. At times able director McCarey seems close to doing it. In the opening sequences the scenes vibrate with the same effervescent youthfulness that the leads are able to exude. But when the complications set in, the whole thing misses the boat. At the fantastic, Wellsian climax, the audience is left with the feeling that Naziism should be left to the tragedians, and that future attempts at comedy should content themselves with less world-shaking themes.