PERHAPS because playwright Bill C. Davis was allowed to rework his own script, the Broadway hit "Mass Appeal" is one play that benefits by moving from stage to screen.

Davis has opened up his two-man drama, adding vignettes and characters that remained offstage in the play. In its expanded form, Davis' comedy/drama becomes an insightful, demystifying look at the Catholic priesthood as a career. It goes behind the pomp and circumstance to show the Catholic Church as a sluggish bureaucracy with its share of personal vindictiveness, and touches tentatively on the cloudy question of sexuality in the celibate system.

But with it all, "Mass Appeal" still remains a cross-generational conflict between two souls. Father Timothy Farley is a clerical charmer, a beloved parish priest doing what amounts to Jack Paar in the pulpit. Farley de=flects uncomfortable questions with a one-liner or a white lie. Snuggled in suburban comfort, he is more concerned with maintaining his popularity with his affluent parishioners than with saving their immortal souls.

Enter Mark Dolson, a brash young seminarian radiant with idealism and bristling with self-righteousness, who feels he has a divine right to antagonize his more worldly associates -- Farley, in particular.

On film -- and perhaps this is screenwriter Davis' fault -- the humorless Dolson seems just too good to be true. But Dolson is no archangel -- a Dark Secret endangers his priestly prospects. So Dolson becomes Farley's cross to bear, and as the older priest tries unsuccessfully to reshape the novice in his own image, he eventually confronts the self-deception of his own "song and dance theology."

Jack Lemmon has taken over the role created on Broadway by bushy-browed Milo O'Shea, presumably because of his "mass appeal" at the box office. Lemmon's Farley is too talk-show slick at first, but with Dolson as a foil, his character warms up about halfway through. With his intense gaze and painful sincerity, fawn-eyed Zeljko Ivanek is quite effective as Dolson. Both actors have climactic, character-revealing sermon/monologues, and each manages to redeem the mawkish words with eye-welling, throat-lumping readings.

Monsignor Burke, the obstacle to Dolson's progress to priest, is the only fully fleshed new character, and Charles Durning makes the addition worthwhile, colossal and full of genially hidden menace.

MASS APPEAL -- At area theaters.