Everybody wants to say something big about the millennium. Within days, the Museum of Modern Art and the Hirshhorn will open big shows dealing with big ideas about the meaning of modernism and beauty, respectively, in the waning century. They'll be joining the Whitney Museum of American Art here, which was out of the gate first with "The American Century: Art & Culture: 1900-2000," two successive mega-exhibitions that split the century down the middle and still filled five floors of the museum--both times.

The first half of "The American Century" (1900-1950) has come and gone. And now the second half (1950-2000) has opened with the daunting, self-inflicted task of explaining how the Cold War, television, the counterculture, immigration, technology, mass media, pluralism, consumerism, feminism, racism and globalization have impacted American culture over the last half-century. And how vanguard artists have reflected those changes in their art.

The first half was better.

Or maybe I just liked the Zeitgeist better. The art in the first show generated some real emotional and intellectual heat, as artists exulted in the machine age, celebrated progress and held a vision of America's future that was upbeat. Even Depression-era artists, writers, photographers and filmmakers stared into poverty's bony face and believed they could make things better. Today, at least in the most recent works in the Whitney show, artists just stare--usually at themselves and often through a lens.

Compared with the first installment, this second Whitney show is a cool stroll through an illustrated textbook, with six "Cultural Sites" that lend social context to the art. Starting in the '50s on the fifth floor with Jackson Pollock and Abstract Expressionism and moving on through Color Field painting, Figurative Expressionism, Happenings, Fluxus, Performance, Video, etc., etc., it tells a familiar tale as it descends chronologically through the building, a different decade on each floor. The layout could be seen as a metaphor for the descent of American vanguard art over the past half-century.

Although short on new ideas, the show does accomplish one thing: Like any good textbook, it does sort out the various movements and trends--especially Pop, Minimalism, Conceptual Art, Post-Minimal art, Performance, etc.--that exploded like land mines in New York and Los Angeles after World War II. No small achievement. It then illustrates these movements with generally good examples and clear and comprehensible text--until it gets to the present decade.

The problem is that many of these examples are now so familiar through reproduction that we no longer actually see them, and focus instead on the narrative text. Basically, the story this show tells is how American art unfolded in the work of innovators like Pollock, David Smith, Morris Louis, Richard Diebenkorn, Robert Rauschenberg, Jasper Johns, Bruce Nauman, Robert Smithson, John Cage, Roy Lichtenstein, Donald Judd, etc. Right up to Bill Viola and Tony Oursler. Adding hundreds of works by hundreds of artists doesn't change the old tale much: It is still about New York taking the lead from Paris and becoming the center of the art world.

There are, to be sure, some unfamiliar, even unforgettable works of art here, including one by Edward Kienholz that marks the beginning of junk assemblage in the early '60s. A hybrid of painting and sculpture, assemblage helped liberate both, removing art from its gilded frame. That shift is represented here by Kienholz's highly charged 1963 tableau titled "The Illegal Operation," built a decade before the Supreme Court legalized abortion in Roe v. Wade. An abortion-rights tract if there ever was one, this assemblage of junk conjures a filthy makeshift abortionist's table fashioned from a broken shopping cart, rags and rusted instruments. That the last woman in this room bled to death is strongly implied. "The Illegal Operation" is the first of many works here that reflect the growing involvement of art and artists in larger social issues.

One of the most remarkable and surprising objects here is "The Rose" by Jay DeFeo, a little-known artist whose work hangs alongside the flags and targets of Johns. DeFeo's craggy, 11-foot-high work is an inches-thick oil painting on wood and canvas once described as "an unnatural attempt to suspend a ton of paint in midair," which it more or less does. Wholly abstract, it seems to beam out rays of light from deep within its dark, volcanic center. A mysterious piece by an equally mysterious woman, "The Rose" took eight years to build (1958-66). DeFeo died in 1989.

This survey does lend perspective: Seen in the broader context of the entire half-century, several works that once commanded ridiculously high auction prices now look merely ridiculous or dated. Especially vulnerable are some of the sillier "conceptual" works (Vito Acconci comes to mind), along with Julian Schnabel's dopey broken-plate painting titled "Circumnavigating the Sea of [Expletive]" and David Salle's 1984 billboard-size dud titled "What Is the Reason for Your Visit to Germany?" (The reason was obviously that a German collector was willing to buy it.)

But while some works lose ground here, others advance in stature. One even becomes a classic. It is Nan Goldin's "The Ballad of Sexual Dependency," a half-hour color slide show with rock and operatic music. I'd seen her photographs of the East Village demimonde for years, but always on gallery walls or in books, and never thought much of them. Here, however, their cumulative power is indisputable. And after years of work, Goldin has unquestionably produced a poignant, tender and definitive document about the artists, drug addicts, battered women and other friends and alienated souls who inhabited New York's East Village in the '70s and '80s.

As for pure aesthetic pleasure--something that hasn't been the point in avant-garde art for decades--nothing approaches Viola's interactive video projection titled "Tree of Knowledge." The only truly beautiful and spirit-lifting contemporary piece in this show, "Tree of Knowledge" creates the sense of an enchanted forest out of one small tree projected on a back wall. And you can make it grow, leaf out, blossom into glorious color and, finally, bear fruit by simply walking down a dark corridor toward it. Get too close, however, and it withers.

It takes some looking to find this little wonder of the video age: It is tucked into a far corner of the second floor, past some of the grosser contemporary video and installation works. Among them is Kiki Smith's sculpture of a crawling nude woman with a 13-foot trail of her fecal matter dragging on the floor behind. She calls it "Tale."

This and other potentially offensive works nearby evoke memories of past conflicts over what is art. And just when we need it, the last of the "Cultural Sites," this one devoted to "The Culture Wars" of the late '80s and '90s, looms before us. It includes a time line of art and its political troubles. It resonates with the first such site in the show, "The Cold War," which is devoted to McCarthy-era witch hunts, blacklistings and banned books.

With uncanny timing, this final site has lined up Andres Serrano's "Piss Christ" (rather beautiful if you forget what it is), Robert Mapplethorpe's ever-astonishing "Man in Polyester Suit" and even a tape of Pat Buchanan giving the speech that brought the term "culture wars" into play. Listen to it.

I left the Whitney thinking more about the culture clashes of the last half-century than about the art. They turn out to be ongoing: That very day the mayor of New York had threatened to withhold funds from the Brooklyn Museum for proceeding with a show he didn't like and hadn't seen.

It was a lesson. History is not a monolith, never has been. It is organic, changing constantly with every newly excavated fact. And recent history--as the Whitney ought to know by now--is the most elusive of all.

'THE AMERICAN CENTURY: ART & CULTURE 1950-2000'

"The American Century: Art & Culture 1950-2000" will continue through Feb. 13 at the Whitney Museum of American Art, 945 Madison Ave. in New York. Tickets are $12.50 for adults and $10.50 for seniors, students and groups of 10 or more. Timed tickets can be purchased in advance (for a $2 service charge) by calling 1-877-WHITNEY or by ordering online at www.whitney.org. Admission on the first Thursday of each month is pay-what-you-wish. Museum hours are 11 a.m. to 6 p.m. Tuesdays, Wednesdays, Fridays, Saturdays and Sundays; 1 to 8 p.m. Thursdays; closed Mondays.