BOOK REVIEW / BIOGRAPHY : The Anguish in His Stories Was His Own : THOMAS MANN: Eros and Literature by Anthony Heilbut; Alfred A. Knopf $40, 688 pages

If there’s a moral here, it’s that young readers shouldn’t be intimidated by masterpieces. Those odd, niggling suspicions they feel--and then disregard as unseemly--may be clues to what the authors really had in mind.

In college, for instance, I was puzzled by how E.M. Forster, in “A Passage to India,” made such a big issue of friendship but was so dry and perfunctory when it came to romance.

And, briefly in command of enough German to read Thomas Mann’s 1903 story “Tonio Kroger” in the original, I was astonished to find that the fearsomely learned Mann--the “Starched Collar,” as his rival Bertolt Brecht derisively called him--had written something much different than what English translations of his other works had suggested to me. In German, Mann sounded plaintive and poetic. He sang.

But what did I know?

Not much but a little, Anthony Heilbut confirms in this massive study of Mann’s life and work. Forster, I learned later, quit writing fiction early in his career because he could no longer do so without expressing his homosexuality.

Born into the wealthy merchant family in Lubeck that he portrayed in his novel “Buddenbrooks,” Mann discovered early on the necessity of--and the price to be paid for--”self-presentation,” or playing a public role at deviance with one’s private yearnings.

In “Tonio Kroger,” Mann stated one of his most famous themes--that artists have a “bad conscience”; that they need to dress impeccably and comport themselves soberly in order to conceal their fundamentally subversive nature.

All the more so if the artist is gay. In the Kaiser’s Germany, homosexuality was illegal. In Hitler’s, it was a capital offense. Even in the United States, where Mann moved in 1938, he feared the ruin of his career. He courted and distrusted the public much as, in the story, Tonio Kroger loves and feels alienated from those paragons of blond, bourgeois normality, Hans Hansen and Ingeborg Holm.

Tonio’s dream, Heilbut notes, “was to marry Ingeborg and have a son like Hans (a typical Mann diversion; the partner he desired was Hans).”

The diversion fooled me, but what Mann didn’t hide was his overwhelming sehnsucht, or longing, which Heilbut calls the wellspring of his work. From the beginning, this deeply inhibited man felt that he had to be content to love beautiful young men from afar--to look but hardly ever touch.

Heilbut shows how this sehnsucht is rooted in Mann’s real-life relationships and expressed in the fictional loves of Hanno Buddenbrook for Prince Kai, Tonio Kroger for Hans Hansen, Hans Castorp for Pribislav Hippe in “The Magic Mountain,” Adrian Leverkuhn for Rudi in “Doctor Faustus”--and, of course, Gustav Aschenbach for Tadzio in “Death in Venice.”

What did Mann’s wife, Katia, and his children think of all this? They were a sophisticated bunch, Heilbut says. The marriage is seen as “devoted,” though “founded on a lie that reverberates through his writings.” Three of Mann’s children were gay; he envied them their openness, and they seem to have communicated fairly frankly.

Heilbut also discusses Mann’s literary influences, from Goethe to Kafka to his brother Heinrich, and the evolution of his politics from World War I jingoism to principled stands against the Nazis and McCarthyism.

“Thomas Mann” develops its main argument--an easy argument to sustain, after all--at sometimes numbing length. Its main value is to turn us back to Mann’s own books--to get us to reread a great but currently neglected writer not as the Starched Collar but as “the poet of the half-open closet.”