Darryl F. Zanuck spent a bundle to make W. Somerset Maugham's masterpiece, The Razor's Edge about the spiritual quest of a WWI vet (Tyrone Power). With thousands of extras and generous French dialogue, rare for Hollywood, the scenes of ''Lost Generation'' Paris boast beaucoup de vérité. (Alas, Zanuck cut corners on Himalayan scenes, with low-cost horizons.) Power stretches himself as a man in turmoil who forsakes wealth and joins the proletariat, while Tierney plays a variation on Scarlett O'Hara as the scheming ex-fiancée who wants him back. Long but seldom flat, the film is terrifically acted, especially by Clifton Webb as a prissy snob who notes, ''I do not like the propinquity of the hoi polloi.'' EXTRAS A commentary, which reveals that director Edmund Goulding supposedly asked Power to abstain from sex so his face would be purged of carnality.