PERFORMING ARTS : COMMENTARY : Lenny the Red Menace : Leonard Bernstein’s liberal leanings kept the FBI busy for nearly 30 years. What was it that made the government so nervous?

Leonard Bernstein, who died at the age of 72 in October, 1990, was many things to many people.

To almost everyone, he was a brilliant, incorrigibly flamboyant, essentially romantic conductor and a facile, conservative, sentimental composer who never seemed to have quite enough time to fulfill his own extraordinary promise.

Bernstein-- Lenny even to strangers--also was a piano virtuoso manque , a knowing lecturer understandably in love with the sound of his own voice, a handsome, all-American arts salesman par excellence , a self-made cultural icon, a committed if not invariably discerning sociopolitical liberal, an unapologetic egomaniac, a playful wit, a chronic over-achiever and, according to two recent biographies, a man of flamboyant ambisexual affinities.

Never mind all that. To J. Edgar Hoover and his intrepid FBI, Bernstein was something else and something worse: a possible Commie.

Yikes.

Bernstein, we are told, posed a potential threat to all things nationally sacred and serene. Call him Lenny the Red Menace.

In the relatively cool light of 1994, it seems like a joke. A silly joke. A bad joke. An expensive joke. A painful joke. But, thanks to four years of perseverance on the part of Allan Parachini, a former Times reporter now with the American Civil Liberties Union of Southern California, no one is laughing.

FBI files, obtained through the Freedom of Information Act after much blood, sweat, tears and delay, reveal that our governmental guardians of virtue spent nearly 30 years spying on Bernstein. The spying, not incidentally, turned out to be incredibly inept and totally unproductive.

It began in 1943. It involved cloak-and-dagger informants, electronic monitoring, surveillance by special agents and a lot of raw-rumor mongering. It took place in New York, Boston, St. Louis and even Los Angeles. The files consist of nearly 700 quasi-literate pages, many of them still partially censored--for reasons uncertain.

All the documents were officially “classified.” Some bore the ominous stamp “secret.”

Bernstein occasionally embraced extra-musical causes that drew him away from the righteous right. He did not invariably check out the lineage of every organization that used his name or accepted his donations. But he swore that he was not a Communist Party member. His lengthy, impassioned disclaimer can be found in the FBI files.

If--horror of horrors--he was a communist sympathizer 50 years ago, the nature of that sympathy was never clearly defined. Nor was the nature of its threat to the survival of our loftiest values.

His opposition to the Vietnam War was never in doubt. That didn’t exactly put him in lonely company.

His fleeting, probably naive association with the Black Panthers at a party in his Park Avenue apartment did little beyond enriching our language with the term “radical chic.” Habitually with-it , Bernstein reportedly said he dug some aspect of the minority cause.

That must have made Hoover and his boys in Washington particularly nervous. Or gleeful. Still, in the end, it didn’t mean much. The ship of state did not sink. Life went on.

Ironically, Bernstein functioned for most of his career as the epitome of that tired cliche, the cultural ambassador. He made friends for himself, for music and, not least, for America, wherever he traveled. The fellow traveled a lot, even in the Soviet Union.

Music may indeed have charms to soothe a savage breast, to soften rocks or bend a knotted oak. Congreve was no fool. Nevertheless, music doesn’t seem able to do much in the long run to corrupt decency or lower morality.

Bernstein’s primary language certainly was music. According to the FBI files, it was Bernstein the man, not his output, that threatened to get him into trouble. At worst, there was some ominous speculation that the pacifist sentiments of his “Mass” might embarrass President Nixon at the opening of the Kennedy Center.

The problem of governmental interference is easiest to define when the subject matter overtly offends political zealots who want to be offended. We were reminded of that danger only this month when the National Council on the Arts overturned photography grants recommended by panels of the beleaguered National Endowment for the Arts. The individuals scorned in this case--Andres Serrano, Merry Alpern and Barbara DeGenevieve--dared to focus their cameras on subjects apparently too indelicate for official sanction: sex and religion.

What is it, one wonders, that makes statesmen, or unreasonable facsimiles thereof, so uneasy about the potentially lofty muses?

When one of Hitler’s cohorts heard the word Kultur , he said he automatically reached for his revolver.

The notorious White House tapes documented Nixon’s particular paranoia about the cultural community. “The arts, you know--they’re Jews,” he declared. “They’re left-wing. In other words, stay away.”

Bernstein was both a Jew and, after his fashion, left-wing. Nixon stayed away from the premiere of “Mass.”

“The FBI owes it to all Amer icans to provide irrefutable, convincing proof that the bureau is no longer doing what it did to Leonard Bernstein,” says Mark Rosenbaum, legal director of the ACLU, “and is no longer trying to cover up such activities.”

The FBI might take a reassuring step in the right direction with the immediate release of the unexpurgated Bernstein files. One wants to know what lies beneath those nasty black blocks that besmirch page after page. Even more, one wants to know what is contained in the 81 pages still missing.

Perhaps the FBI thinks it is practicing damage control, or belatedly protecting decorum, by deleting references to Bernstein’s sexual proclivities. If that is so, the exhaustive books by Joan Peyser and Humphrey Burton make any such effort obsolete.

Perhaps the FBI feels an aura of noble secrecy must be maintained to justify its snooping. If that is so, the ancient excuse invoked--”national security”--has been stretched beyond credibility, and beyond moral conviction.