The typical modern American musical flounders around happily and loudly in the realm of brassy mediocrity. A star or two nearly inevitably thrusts his or her personality into the affair in order to please the expense accounters and fill up the marquee--and, of course, to drag the smiling mess along. There are occasionally a few minutes' worth of tolerable or colorful or amusing songs and/or dance routines. There is nearly never much of a plot, nor is there much acting.

The simple reason for mentioning all this is that Jamaica is terribly typical.

The show has bright spots--Oliver Smith's ingenious scenery for a glass-bottom boat scene--and it is generally pleasant, but despite its effective advance publicity here and in New York, it is neither an outstanding example nor an extension of its genre.

Although there is lots of body and little clothing in Jamaica, the choreography seems merely mass-produced, and only mildly erotic. Even bodies cannot hide the basic, familiar fault: the book is hollow. On a tiny island near Jamaica, Koli, the chief fisherman, and Savannah, the most eligible young woman, have a bumpy time getting married. They like each other. They don't. They do. They don't. A rival comes. Then a hurricane. Maybe Koli's drowned? She loved him along. He's saved. New doubts. New quarrels. Final reconciliation.

Lena Horne, excellent in and by herself, does not act well enough to carry interest into the plot. She sings as well as ever, particularly in "Push The Button," a satirical comment on Manhattan (there's a little island on the Hudson. . .), "Ain't It The Truth," and "I Don't Think I'll End It All Today." She can ride one word onto several notes as perfectly as she can move her body provocatively. Unfortunately, she has trouble weaving in and out of a Jamaica accent, often waiting to lean into Caribbean pronunciation and rhythm until just before a song begins.

Ricardo Montalban, as Koli, fills the role, but with nothing special. He has one good song, a Calypso mockery of mankind called "Monkey in a Mango Tree." Josephine Premice, as the opportunistic second-to-most-eligible female around, is first rate, especially in "Leave the Atom Alone," an amusing try by the show's authors to be socially significant. Ossie Davis does well as her occasional beau, Erik Rhodes as the exaggerated British governor of the island, Augustine as a lovable urchin, and Adelaide Hall as a homey, cloud-reading sage.

They all fit together competently, and they all smile well.