I doubt that Warner Bros. will be overjoyed to hear this, but Spike Jonze's most soulful Maurice Sendak movie isn't his $90-million-plus version of "Where the Wild Things Are" but a 40-minute labor-of-love documentary about Sendak that premieres tonight at 7 p.m. on HBO East and 10 p.m. on HBO West. Titled "Tell Them Anything You Want: A Portrait of Maurice Sendak," the film, co-directed by Jonze and Lance Bangs, is a mesmerizing portrait of an unsettled artist as an old man. You know right from the start that it's not going to be a reverential, Ken Burns-style film. Our first glimpse of Sendak reveals a wild-eyed oldster, shakily leaning on a cane, his speech liberally sprinkled with profanity.

When Jonze asks if he has any advice for young people, Sendak brusquely replies: "Quit this life as soon as possible. Get out. You're doing a documentary about a brain-dead person."

Jonze is savvy enough to realize that Sendak is such a peculiar, self-dramatizing character that the best thing for a filmmaker to do is stay out of his way as much as possible. So except for one marvelous glimpse of Sendak, on a bright spring day, walking with his dog, surrounded by a jungle of lush greenery that makes him look like a character straight out of "Wild Things," the film is wonderfully informal and unadorned, with most of the footage simply shot in Sendak's living room (which has a cardboard stand-up of Barack Obama in the corner).

For all the cleverness and sharp-eyed originality in his work, Sendak turns out to be an unhappy guy, haunted by what he calls a "permanent dissatisfaction" in his life. Unwanted by his parents ("I was not intended -- it was an accident," he insists) and blessed with few social skills, he spent most of his time as a child alone, sitting at the window, drawing children playing in the street. He adored his older brother and sister -- he still talks about them with awe today -- but he was always an outsider, especially once he realized that he was gay, not an especially easy sexual orientation for a children's book artist in mid-20th century America.

As he bluntly puts it: "I didn't want to be gay. It was yet another sign of isolation. It was something that you hid.... It was extremely bad news."

To Jonze's credit, he puts Sendak so at ease that the older artist willingly reveals his innermost fears and extravagant fantasies on camera, the same fears and desires that clearly shaped him as an artist. In one extraordinary scene, Jonze films Sendak reimagining his mind-set as an ambitious young artist, almost greedy for success. "I want to be famous, I want to be snooty," Sendak says, reconnecting with his younger self. "I want to have a big, gray shiny car and everybody will see it. Here comes Big Mo! Holy [moly]. It's him, it's him! Sure I'll give you an autograph, you [expletive]."

It's no wonder "Anything You Want" has already been short-listed for the Oscar for best documentary short. It captures a great performance, sometimes comic, sometimes bittersweet, from an fierce old man, afraid of dying, but with an indomitable will to live. At one point, Jonze shows us a montage of Sendak's death-obsessed proclamations, concluding it by telling him, "You've been claiming you're dying and becoming senile for years -- and it hasn't happened yet." To which Sendak replies, with supreme self-assurance: "But it's gonna!"

After seeing Sendak in the flesh, it's easy to understand why Jonze was inspired to spend so many years wrestling with his adaptation of "Where The Wild Things Are," even though it's just as easy to see why the spirit of the book proved to be so difficult to capture on film. Even though he's a filmmaker from a very different generation, Jonze instinctively understands that Sendak is one of those timeless artists, a true original whose work digs far deeper than most of the reassuring and hopeful sentiments expressed in most children's literature.

Perhaps that's why Jonze ends the film with a question taken from a page of one of Sendak's books. It's a question that artists ask themselves all the time, although we mere mortals could puzzle over it for the rest of our lives as well: "Do you always want what you think you want?"

Photo of Maurice Sendak in "Tell Them Anything You Want: A Portrait of Maurice Sendak" from HBO.