IT'S about time.

Today, a smashing, well-selected show of recent abstract paintings by Washington's Sam Gilliam opens at the Corcoran Gallery of Art.

Gilliam is local, Gilliam is black, and he often is described, not without good reason, as a second-generation Washington Color Painter. All this has worked against him. He is an extraordinary artist. But though moderately prosperous and moderately famous, Gilliam, at 50, has failed to receive--from the New York big-bucks market, or the glossy magazines, or the Corcoran itself--the recognition he is due.

The Corcoran's exhibit is an effort to correct that.

"This show," insists John Beardsley, the young free-lance curator who picked the pictures, "was not intended as a sop to those who have complained about the Corcoran's commitment to good local art. Nor is it an affirmative action show."

When Beardsley praises Gilliam, he does not pull his punches. These pictures from the '80s, the catalogue contends, "are unquestionably the best" of Gilliam's career. When Beardsley writes that "Gilliam has always been a good painter," he is setting up his end-of-the-essay clincher: "Gilliam is now a world class painter."

There is in that ringing claim something unconvincing. It suggests some recent breakthrough, as if Gilliam, at last, had managed to escape the provincial mire of merely local art. None of that will wash.

Gilliam has not suddenly become a major modern painter. He has been one for years.

His originality, his fire and his high ambition all have been apparent since the 1960s. His art may have grown stronger, but it did not do so suddenly. All of its improvements have been incremental. By his loyalty to abstract art, to Euclidian geometry and highly complex color, Gilliam, here as in the past, declares himself forthrightly a Washington Color Painter.

In his cutting and his pasting one sees the debt he owes to the late Howard Mehring. His triangles and circles recall Kenneth Noland's. Gilliam has never tried to break away from the nourishing traditions of Washingtonian abstraction. Instead he has extended them, and added to them boldly. He still paints in series, as he used to do for his Jefferson Place shows. His raked surfaces are richer now, his colors may have deepened, but the battle that one senses at his paintings' core is anything but new.

It is a struggle between opposites, between chaos and control, between the intuitively improvised and the predetermined. In every picture here, one can find the circles, the triangles and squares of Washington Color Painting--and of L'Enfant's city plan. These shapes are never sloppy, their arcs are compass-clean, their right angles are true, but all of them are countered by a freedom, an abandon, that takes the breath away. Geometry, for Gilliam, is what melody was for John Coltrane, something to be stretched, cracked or contradicted. The rigorous in Gilliam's art is always, and amazingly, balanced by the passionate, the played-by-ear, the free.

His show has been installed in four discrete parts: In the Corcoran's rotunda, Gilliam has installed a circle-stating, circle-breaking, 13-panel work, painted for this show, which he has titled "Rondo." Next come four fine paintings from the 1980 series Gilliam calls "Chasers." Each "Chaser" in the series has an arc at upper right that is balanced by a rectangle that floats at upper left, and each one has been stretched on a nine-sided support. Then come the "Vertical 'D's' " of 1982, a 21-painting cycle of tall rectangles, each six feet high, each notched, at lower right, by a D-shaped form of metal fired with enamel. The exhibition ends in grandeur with huge pictures from 1981. He calls them "Red and Black."

All the paintings at the Corcoran--and the new works he calls "Z's," now at Middendorf/Lane (2009 Columbia Rd. NW)--are hugely energetic. No earlier Color Painter ever managed to come up with surfaces so sculptural or with layered colors so constantly surprising. Gilliam's pinks could not be hotter, his greens could not be leafier, his deep blues and blacks recall the midnight sky.

In their multiple allusions, too, these complex works transcend, and at times demolish, the minimalist esthetic in vogue in the '60s. All the abstract paintings hanging at the Corcoran, except perhaps the "Chasers," hint at figuration. One does not have to stretch to see hot suns and ringed planets floating there in deep blue space behind the flying shards of color that activate his "Rondo." The human-scaled "Vertical 'D's' " stand there on their jutting feet like so many saints in a Byzantine mosaic. And their details--their open squares, their Suprematist voids and arcs, and that Braque-like bird--suggest a whole history of art.

This sense of complex content, of half-concealed story, is strongest in the "Red and Black" series. These big pictures feel like skyscapes or landscapes. One of them, called "Elm," comes complete with trunk and leaves and, half-seen through its branches, the hugeness of the sky. "The Arc Maker I and II" seems to be, like "Rondo," a picture about outer space. Gilliam's reds and blacks are more than colors, they are signs--for blood and death, for fire and for soil.

"Gilliam seems fully to express the passionate, accretive, richly layered aesthetic avant-garde impulses of our time, and moreover to synthesize traditional American abstraction and a distinctively black American chromatic dynamism," writes the Corcoran's Jane Livingston. They hint at more besides, at plants and orbs and city streets, at pyramids and flight. But it is, beyond their fullness, their rightness one remembers most.

The Gilliam exhibit is the latest in an admirable series, "Modern Painters at the Corcoran," sponsored since 1977 by the SCM Corp. Yes, the Gilliam we meet in this splendid show is indeed a world-class painter working at full stride. For those who've watched him grow that is no surprise.