Irving Berlin is so American he makes apple pie look almost "un." Despite roughly a quarter century out of the public eye, he remains vibrantly alive in the public ear. And in the syncopated beating of the public heart.

If America were a show, the credits would say, "Music and lyrics by Irving Berlin."

Berlin's extended self-exile -- holed up in his town house on Beekman Place in New York -- has become rather notorious, and when he celebrates his 100th birthday on Wednesday, it's likely none of us will get a look at him. But it's good to know he's still around -- that this living link to the richest traditions of Tin Pan Alley, Broadway, Hollywood and the immortal Lower East Side of Manhattan continues to exist.

After all, he made a promise in 1925: "Days may not be fair, always; that's when I'll be there, always."

The man seems a mystery, but his work does not. It's so basic, so accessible, so solid. The term "standard" has the unfortunate connotation of "ordinary"; none of the innumerable Berlin standards is. Even when his lyrical references to turkey trots and Morris chairs date, the melodic invention remains fresh and catchy.

And though one may think of Berlin songs as predominantly positive and upbeat -- "Come on along, come on along, let me take you by the hand" -- through many of them wafts a strain of plaintive melancholy, something introduced, so legend has it, after the death of Berlin's first wife:

"Remember we found a lonely spot, and after I learned to care a lot, you promised that you'd forget me not? But you forgot to remember."

What special qualities do Berlin's songs have? "Elusive, I think," says Bobby Short, the greatest cabaret singer, who's performed many a Berlin tune. "His work is not witty, but it is very down-to-earth. And amazingly natural. Not that they're all so simple; 'Puttin' on the Ritz' and 'Top Hat' and many of the others are very complex things. He had a great feeling for jazz and for so-called 'Negro music.' "

Indeed, a Berlin myth for years was that Berlin was so prolific, he had to have -- in the parlance of the time -- "a little colored boy" writing songs for him. Berlin did hire pianists to take down melodies, but not to create them. "Rodgers and Hart even went so far as to put the myth in a song, 'There's a Boy in Harlem,' for a movie called 'Fools for Scandal,' " says Short.

That was not the only Hart lyric to contain racist references. By contrast, says Short, "Mr. Berlin was one of the first of the Tin Pan Alley composers to pay attention to the social injustices of the time. A song he wrote called 'Supper Time,' for Ethel Waters to sing in 'As Thousands Cheer,' about 1933, was sung to children whose father was being lynched.

"When it's performed now, people see it as about an old woman who simply lost her man, but if you look carefully at the lyrics, that's not what it's about."

As for the imaginary collaborator, Berlin would joke about it himself. He would hand a producer a copy of a new song and say, "This is one 'the little colored boy' wrote that I found in my trunk." And laugh.

"The main thing about Berlin is that he inspired a lot of envy in all other composers," says Mark Sandrich Jr., a composer himself and the son of the director of "Top Hat," "Carefree" and "Follow the Fleet," classic Astaire-Rogers musicals with Berlin scores. "It all seemed to come so easy to him, as if he never had to work at it -- though of course he did. The melody and the lyric always went just the way they should, like water running down a hill.

"His songs didn't have any seams. They didn't feel like anybody ever wrote them. It was as if Berlin just walked down the street and heard them, and they had been there all along, and he just had to reach up and pluck them out of the air."

As a child in Beverly Hills in the '30s, Sandrich, 60, remembers hiding in the family study on Roxbury Drive so he could eavesdrop when Berlin came by to show off his latest compositions on the piano in the living room. Jerome Kern lived nearby and Ira Gershwin's place was up the street. These were gala times.

"Once at the dinner table, my father asked him what was his biggest hit, his most successful song," Sandrich recalls. "And Irving said, 'Blue Skies.' Well, that surprised us, since the song was 10 or 15 years old at the time. And he said, 'As a matter of fact, any time I want, I could have "Blue Skies" Number 1 on the Hit Parade.'

"We thought it was very odd, very unlike him, to say something so boastful, and we just said, 'Yes, yes, sure.' But he went out and got Tommy Dorsey to make a record of 'Blue Skies' and not long after, there it was, Number 1 on the Hit Parade. He said, 'I could have lived my whole life on that one song.' "

For "Holiday Inn," the 1942 Bing Crosby musical that Sandrich Sr. directed, Berlin wrote a collection of tunes keyed to various holidays. "We were driving him to the airplane one night," Sandrich Jr. recalls, "and he sang the one for Valentine's Day, 'Be Careful, It's My Heart.' But neither Irving nor my father was happy with the Christmas song. Irving said, 'I have something in the trunk. I think I can work it out.'

"A few days later, he called from New York and played 'White Christmas' over the telephone. I listened in on the extension. My father loved it and decided to revamp the whole film to build it around that song."

It may be the most indelible of all Berlin's hardy perennials, and it quickly became the big emotional favorite of World War II. In an interview for Charles Thompson's biography "Bing," in 1976, Crosby recalled, "I sang it many times in Europe in the field for the soldiers. They'd holler for it; they'd demand it. And I'd sing it. And they'd all cry."

In 1945, Mark Sandrich died. His son remembers that as the last year he saw Irving Berlin. He phoned Berlin in 1963 when in New York working on his own score for the musical "Ben Franklin in Paris," starring Robert Preston. Sandrich's mother, Freda, 88, called Berlin last year when he turned a mere 99.

"My husband revered, admired, loved, adored working with him," Freda Sandrich says. "They became very close friends. Irving's wife Ellin is a very bright woman, with a wonderful wit. She had a marvelous party once for Roosevelt. I think it was at the Trocadero. My husband hated big parties and he said, 'Oh, Ellin, please don't invite us!' "

She sent Berlin a note for his 100th birthday and plans to phone him the day after, when he's not so busy celebrating. "I remember him as being very delightful, very warm and pleasant," she says. "I think that Irving used to write -- his lyrics especially -- to the erudite as well as to the untutored. I felt that way. And that, for me, was his philosophy. The simplicity of it was the wonder of it."

Mark and Freda's other son, Jay Sandrich, is the director of "The Cosby Show," a hit that Berlin has confided he enjoys and admires.

For all the recognition and acclaim he received, and despite the enormous popularity of his work, Berlin remained uncertain and insecure. In 1954, when he emerged from one of many semiretirements to write new songs for the Crosby film "White Christmas," Berlin told an interviewer, "I thought I was finished. I thought I'd had it as a songwriter, but I was just tired.

"I had spells of great depression, and the only thing that could get me out of it was going back to work. It was as simple as that."

Mark Sandrich remembers Berlin as having suffered feelings of inferiority. He was a self-taught musician from the Lower East Side, who'd worked his way up through Bowery nightspots, and who'd peddled his songs like a salesman. He wasn't a tony show composer and Sandrich says he was the victim of some industry "snobbery" for that reason.

"As far as the composing goes, there was a kind of modesty about him. He really didn't think he belonged in a class with Kern or Gershwin or Rodgers and Hart. He had this feeling he didn't belong in their class. It used to drive my father crazy. He would say, 'Damn it, Irving, you're a perfect composer! You know just what you're doing!' "

Why didn't Berlin listen to the admiring words of his colleague Cole Porter: "You're the top! You're a Waldorf salad. You're the top! You're a Berlin ballad."

There was strong resistance at RKO in Hollywood to bringing Berlin out from New York to do the music for "Top Hat," Sandrich recalls, because he was considered just a songwriter, not among the elite fraternity of show composers. Doubts persisted about the score's worth even up to the first public preview of the film -- incredible when one considers it contained "Cheek to Cheek," the title song, and the beguiling "Isn't This a Lovely Day (To Be Caught in the Rain)?"

Not quite the happy ham that George Gershwin was, Berlin nevertheless became accustomed to performing his own songs when still pitching them along Tin Pan Alley. He has, by all accounts, a wee small voice, thin and high, and the only key in which he could play the piano, F-sharp, was really too high for him.

He did have three or four customized pianos made with levers that allowed him to change the key even while hitting the same (mostly black) notes. Berlin gave one to the Smithsonian in 1972.

However tiny the voice, Berlin performed the Berlin songs with gusto. More than one wag has been credited with the observation that when he sang, "you had to hug him to hear him." For the 1942 movie version of his military revue "This Is the Army," Berlin himself appeared -- summoned forth by George Murphy (with Ronald Reagan in the wings) -- to sing his World War I hit "Oh, How I Hate to Get Up in the Morning."

He looked like a little old man even then.

Most everyone has a personal Berlin favorite and a preferred rendition. Definitive though Berlin's version may be, the voice I hear when I think of "Oh, How I Hate to Get Up in the Morning" is my mother's. She sang it to my sister, my brother and me when rousting us for school, back in the Midwest of the 1950s.

Under the circumstances, we may not have fully appreciated hearing it. In retrospect, it was wonderful. Irving Berlin wrote songs to be sung from stages and screens and recordings, but he also wrote songs for moms to sing to their kids.

Not everyone savored hearing Berlin sing Berlin. In his anecdotal history of the Friars Club, "B.S., I Love You," Milton Berle remembers encounters early in the century between Berlin and John Philip Sousa, the march king. Berle quotes Sousa as having once said, "Irving sings a song like the composer never had a father."

Berlin was "small and thin," Berle recalls, "and even in his thirties, looked as if he had twenty-four hours to live." At Berle's earliest visits to the New York headquarters of the Friars in the twenties, he recalls round tables at which would sit George M. Cohan, Gentleman Jim Corbett, Enrico Caruso, Fred Allen, Eddie Cantor and Berlin.

Never saw the sun shining so bright. Never saw things going so right.

Attempts by the outside world to reach Berlin in more recent times have mostly proved futile. Ed Sullivan got him to appear for a TV tribute (with Kate Smith, naturally, singing "God Bless America") in the '60s. But because he refuses to travel to Washington to accept the prize, the board of trustees refuses -- foolishly -- to give Berlin one of the Kennedy Center Honors.

For his 1973 book "They're Playing Our Song," a lively dissertation on American pop, Max Wilk induced Berlin to grant a short telephone interview. The composer was not precisely convivial. "You're wasting your time," Berlin told Wilk. "Nobody ever wants a songwriter to talk. All people want to hear is his music.

"Besides, who cares anymore? There's a whole new public out there, and they don't even know people like me are still around. Don't you read the papers? We're antiques, museum pieces. Today, it's all kids." And, he added, "Most of us songwriters are terrible liars anyway."

Today's songwriters often perform their own material, and the songs are supposed to be their innermost expressions. While some of his brooding ballads appear inspired by his own experience, Berlin rejected the idea that a composer writes songs to please himself.

"I write a song to please the public," he told Wilk, "and if the public doesn't like it in New Haven, I change it!" New Haven was where Broadway shows traditionally tried out before opening in New York.

He saw himself as a public servant, in a way, and Berlin's incomparable commercial success owes much to his keen ear for public tastes. When he first played "White Christmas" for a group of reporters, he included the original verse: "The sun is shining, the sky is blue, the palm trees gently sway; there never was such a day, in Beverly Hills, L.A. But it's December the 24th, and I am longing to be up North."

The reporters looked baffled by the references to palm trees and Berlin sensed it. According to Wilk, he immediately gave orders to eliminate the verse from all sheet music. The verse is rarely sung to this day. Nor was it part of Bing Crosby's original, all-time-best-seller recording.

Fear of failure seemed to dog him. In a 1958 interview, he complained, "The toughest thing about success is that you've got to keep on being a success." He is still alert to what he considers misuses of his songs, and lawyers help enforce his wishes.

"Years ago I made a recording of Berlin songs, some of them rather obscure ones, for Ben Bagley," Bobby Short says. "And Berlin was enough on the ball to call Ben Bagley up and voice his criticisms about this and his complaints about that."

Berlin declined permission to include songs whose copyright he controls to be used in the MGM compilation film "That's Entertainment!," fearing the worst. But when he saw the film and liked it, old pals from Hollywood, including one-time MGM music director John Green, persuaded him to give permissions for the sequel, "That's Entertainment, Part 2." Thus did Fred Astaire and Judy Garland parade about in tramp togs singing "A Couple of Swells" from the all-Berlin extravaganza "Easter Parade."

What Berlin's songs often celebrated, explicitly as well as implicitly, was music. Surely no composer ever wrote more songs with music references in the titles and lyrics: "Say It With Music," "Let Me Sing and I'm Happy," "Play a Simple Melody," "A Pretty Girl is Like a Melody," "Soft Lights and Sweet Music," "Where Is the Song of Songs for Me?" and "The Song Is Ended (But the Melody Lingers On)," among others.

For his book, Wilk unearthed a Berlin verse written circa 1913 and published as part of a commemorative menu at a beefsteak dinner held by the United Songwriters of America, a precursor of ASCAP. It indicates Berlin underestimated his art and his craft even then:

Popular song, you will never be missed

Once your composer has ceased to exist,

While Chopin, Verdi, Beethoven and Liszt

Live on with each generation.

Still, though you die after having your sway,

To be forgotten the very next day,

A rose lives and dies, in the very same way --

Let that be your consolation."

Only a couple of years later, Berlin was writing what would have to be considered a very premature epitaph for himself, "When I Leave the World Behind." The verse says, "I haven't any gold to leave when I grow old," which hardly applies. The chorus concludes:

"I'll leave the nighttime to the dreamers, I'll leave the songbirds to the blind; I'll leave the moon above to those in love; When I leave the world behind, when I leave the world behind."

Nearly half as old as the young country to which he came from Russia, as Israel Baline, in 1892, Irving Berlin is not just American music, as has been said, he really is music, period. Perhaps in his isolation, tunes still occur to him, and verses form in his brain, and a rose may bloom on Beekman Place.

Surely the worries and the insecurities are ancient history by now. He need only open a window on Wednesday to hear the world singing the songs, and thereby singing the praises, of Irving Berlin. Blue days? All of them gone. Nothing but blue skies from now on.

Not for just an hour. Not for just a day. Not for just a year. But always.