NEW YORK - The musical On a Clear Day You Can See Forever has undergone a sex-change operation. When it opened on Broadway in 1965, it was about a woman named Daisy with a distinct hidden 18th-century personality named Melinda - and the psychiatrist who falls in love with Melinda, the alter ego.

It opened again Sunday night on Broadway, a completely reconsidered show. Now it's about a man named David with a hidden 1940s personality named Melinda - and the psychiatrist who falls in love with Melinda, the alter ego.

On a Clear Day You Can See Forever has also undergone a change in sexual orientation. The new David is gay, and when the shrink falls in love with the character he unlocks from David, the charming and beautiful Melinda, is he really falling in love with. . .?

Well, you get the picture, even if audiences may find it spotty. The plot was tough in 1965, without all the sexual confusion that in fact gives the plot new depth - even as it makes it harder to believe. Except for the memory scenes with Melinda, On A Clear Day was set then in the '60s. It's update takes place in the mid '70s, still with Alan J. Lerner's lyrics and Burton Lane's lovely music, although some of it was not in the original and much of the rest has been moved around to nicely fit the new plot.

Lerner's book for the show has been rewritten by Peter Parnell and the new version is the vision of its director, the nervy Michael Mayer.

When it opened in 1965, never to be revived until now (if this wholly different concept can be a revival) it starred Barbara Harris at Daisy/Melinda and John Cullum as the shrink. It was high-concept - we didn't have that phrase for it then - and lasted for only 283 performances.

I saw one of them. I was a freshman at Temple University and hopped a train - the Pennsylvania Railroad, then - to buy a cheap balcony seat, an elaborate ploy to ignore studying. Those were the days when show tunes got air play, and I had heard and liked not just the title song, but two break-outs: "What Did I Have That I Don't Have?" and "Come Back to Me."

I can remember being swayed by the tunes, startled by the plot. Or maybe just naïve. Back then, a show with a psychiatrist - especially a musical that transitioned from multiple personalities to a consideration of reincarnation - seemed alien.

Nowadays, when the Travel Channel is ripe with shows about the paranormal and psychic phenomena, incarnation is yesterday's transformation. But a musical about it, involving a psychiatrist who is an unethical mess and a patient-abuser besides, is still an outsider idea - especially when it demands that we feel for the guy.

For me, On a Clear Day is still a lot of psycho-babble set into a framework of bunkum. That said, it's hard not to like the ever-appealing Harry Connick Jr. as the psychiatrist, or the fabulous Broadway newcomer Jessie Mueller as the alter-ego he loves, or the engaging David Turner as the gay floral arranger who houses this woman in his mind.

Certainly, Mayer had a clear idea of what he wanted in directing it; this Clear Day has a substantially tighter book than the first, and its unfailing '70s look - kaleidoscope wall patterns and flower-power bell-bottoms and plenty of orange - puts you right back into the era. And makes you think of some of the really great musicals then.

--------------------------------------

Playing at the St. James Theatre, 246 W. 44th St., New York.