The passage of time has faded Finian's Rainbow. Its fantasy minces, its humor stumbles, its message plods. Its plot--which genially ignores internal consistency throughout--soon divests itself of every shred of plausibility and rushes headlong into a happy ending.

And yet its music is appealing, exciting, frequently lovely. Even the lyrics (by Yip Harburg, who collaborated on the book) are clever, far better than the dialogue. If the play, which premiered in 1948, usually seems about ten years older than it is, many of its songs, at least, have broken free of time altogether.

Quincy House has not only taken on this odd melange but battled against a leprechaun-sized stage and an orchestra with two three brass instruments for every stringed one. It acquits itself honorably, but it does not quite win.

No doubt the lassitude that overhung much of the show last night was temporary and correctible. Actors can be encouraged to deliver their lines with more conviction, members of the chorus told to feign interest in what they're singing, light and curtain cues picked up, the entire show made faster, snappier. The audience last night wasn't the sort that can energize a cast; it had, after all, passed up both "a tragedy of sex" and an original play for adults only in order to see a 20-year-old musical comedy.

But even with a more responsive audience, problems will remain. George Rosen is always droll as Finian, a dotty old Irishman who has stolen a crock of leprechaun gold and buried it near Fort Knox, an area he believes conducive to spontaneous generations. Carolyn Firth, his ready, nubile, and willing daughter, is a pretty girl and a charming actress. But neither of them seems quite at home in a brogue; Rosen at times simply deserts Belfast for Brooklyn. And Miss Firth, for all the attractiveness of her voice, shares with many of the other singers a tendency toward inaudibility.

Neil Miller's orchestra, which is fine when it's blaring forth the overtures, sounds embarrasingly thin during quieter numbers like "How Are Things in Glocca Morra" and "Old Devil Moon." Wendy Philbrick's choreography--except for the genuinely funny beginning of Act II--seems humdrum, and fuller of to-ing and fro-ing than the quarters permit. And in a play about better race relations, it's unfortunate that a late line of dialogue, rather than the makeup, informs us that most of the chorus of sharecroppers is supposed to be Negro.

Randy Lindel, as the colleen's Missituckian beau, and Peter Houghteling, as the bigoted legislator, Billboard Rawkins, were adequate but little more. William Hodes, as Og, the rightful owner of Finian's gold, displayed a physique as unelvishly robust as his singing voice (he spoke in a coy falsetto). Other members of the cast, however, were more successful.

Besides Miss Firth and Rosen, I liked Richard Cooke, as a henchman of the demagogic Southern senator who wants to dispossess the poor but tolerant folk in whose valley Finian has sunk his funds; Pat Wynn, as the hero's graceful kid sister who, being mute, dances to communicate (don't worry, she'll learn to say "I . . . love . . . you" before the curtain; and Steve Presser, in the small role of a cigar-chawin', bulge-bellied minion of the law.