In Saturday Night and Sunday Morning, Britain's lavishly praised man-bites-dogma story of a young rake's progress at sabotaging is society's large-bore canons, the protagonist is played with elemental eloquence by Albert Finney, the brass-bold, porridge-plain son of a Lancashire bookie. Improbably enough, Saturday's hero has also been acclaimed as the finest new Shakespearean actor since the debut of Sir Laurence Olivier. A versatile veteran of two seasons with the prestigious repertory theater at Stratford-on-Avon, 25-year-old Finney is a man of many parts indeed: master of a Methodically naturalistic acting style and a range of dicition from Cockney to King's English. Unequivocal on the subject of success, he relishes the bread but not the baloney of matinee idolatry, shuns night life, owns little more than the wardrobe on his back. A rebel with but one cause, the solitary actor is committed to his craft with missionary zeal, will soon doff the sackcloth of Martin Luther (in John Osborne's latest London play) for the velvet of Tom Jones, a color filming of Fielding's ribald classic. Then back to the Bard for another season on the boards. "When I'm old," he says, "I want to be sorry for what I've done, not for what I haven't done."