Latest in the never-ending stream of De Mille productions, "Union Pacific"-- now at the Met--is like all his others in the grand scale of its theme and the fragmentary method of presentation. The cast of thousands, the romanticized history, the premeditated lavishness and panoramic effect--these are all present. But the story, which concerns the building of America's first transcontinental railroad, is amenable to this sort of treatment; and the screen version has been made with unusually great attention to detail. As a result, the atmosphere of frontier times--composed of the amusing savagery of the Indians, their reaction to "civilization," the lives of the railroad workers, and the machinations of big financiers behind the scenes in Washington--is vividly portrayed. Technical superiority, shown particularly in the handling of minor characters, has produced an authentic background; Akim Tamiroff, as a virile plug-ugly, is outstanding. To be sure, as much cannot be said for Joel McCrea and Barbara Stanwyck, who are pleasant but unnecessary; nevertheless, by virtue of the skill with which a worthwhile tlicme has been handled, a convincing and certainly entertaining motion picture has been produced.