"A Month of Sundays," a new musical based on a comedy by Victor Wolfson, has to do with the machinations of an amiable old excursion boat skipper, who goes to rather bizarre lengths to keep his condemned ferry from being converted into a garbage scow. After two hours with his passengers one can be pardoned for wondering why he doesn't just turn the damn thing over to the Sanitation Department.

Instead, the Captain (played by Gene Lockhart) is weasled into taking his passengers on a jaunt to an island in the Caribbean, where life can always go on being Sunday. Unfortunately, nasty old Reality (in the shape of a U.S. Coast Guard cutter) intervenes, and there are oblique hints that you just can't escape from life.

Perhaps it's just as well that the plot is practically non-existent until near the end of the second act. For its first three-fourths, the play is simply a below-par musical revue, a series of mediocre songs and dances unhampered by any connecting thread. Indeed, Jo Mielziner's one set does remind you that this is all taking place on a rather battered Showboat, but there is no other perceptible connection with the sea.

Nancy Walker, the female comic lead, is probably the loudest and most un ingratiating actress on the stage today; Gene Lockhart, her co-star, is an established actor in his own right, but he has no singing voice, and this is, unfortunately, a prerequisite in a musical. There is, of course, a romantic sub-plot running through the play, but since neither of its principals can either sing or dance, it seems hardly worth mentioning.

"A Month of Sundays" perks up a bit in the second act with a couple of lively tunes, but none of Albert Selden's music is really melodic; the book and lyrics by B. G. Shevelove are equally uninspired.