AARON SISKIND'S photos of Harlem in the 1930s, on view at the National Museum of American Art, are dispiriting. Earnestly and honestly contrived, most of them depict people whose future was already past.

This is not the vibrant and vital "Black Capital of the World" that was celebrated in the Harlem Renaissance. This is the bleak urban wasteland of the underclass where "Nothing's happening," as photographer Gordon Parks says in an introductory note to the catalogue. "Nothing's shaking up or down the line."

Parks, himself one of the most famous of Harlem's success stories, says Siskind's photographs are "a mirror of my own past . . . . Those same tenements that once imprisoned me are still there, refusing to crumble, holding other restless black boys for sentence without trial."

Something important has crumbled, however. Siskind's three photo projects, collectively known as the "Harlem Document," were an early product of the alliance of white liberals and black activists that won the civil rights war and then swiftly decayed into acrimony over ethnicity, empowerment and entitlements. There aren't many warmhearted Jewish schoolteachers like Siskind roaming today's Harlem with cameras hung around their necks.

But in fact Siskind was no less an outsider in those streets and tenements half a century ago. Most of the people in these photographs are stiffly posed, yielding to the camera only the veiled expressions that African-Americans have always used to shield themselves from whites, whether they be bosses or benign intruders. The pictures could have been taken today, although the kids wear Nikes now and the dudes hide their self-doubt behind sunglasses. But decency and determination still struggle against rage and despair.

The photographs are artfully composed, technically excellent and speak for themselves, as they must because most of the scenes and subjects are unidentified. We can't help wondering what has become of these children playing in the streets, these young men standing on the corners, these young women dressing for dancing or church, in the years since Siskind sought them out. And we can't help fearing that we probably know.

AARON SISKIND: Harlem Photographs 1932-1940 -- Through March 17 at the National Museum of American Art, Eighth and G streets NW. Open 10 to 5:30 daily. Metro: Gallery Place.