John Walker is an abstract painter of singular power, fully in possession of his craft. As an artist and much-admired teacher, the British-born Walker has been influential. Yet his current show at Knoedler is disconcerting. The exhibition, a sampling of mammoth abstract collages from 1974-78, together with current work in the same medium, is beautiful and brutal in equal measure.

First impressions are breathtaking. In the main gallery, your eye is pulled immediately to the two 10-by-8-foot paintings – painted canvas collages – structured on a majestic ordering of blues and yellows: “Ostraca I” (1977) and its untitled pendant piece from the same year.

The architecture of the work overwhelms with the coloristic rhythm of its recessions and advances. Hardedge pieces of painted and cut canvas shift and jostle for position like tectonic plates. Ignoring Clement Greenberg’s gospel of flatness, Mr. Walker is a gifted exponent of spatial depth. So difficult to achieve, this is what makes these arrangements particularly memorable.

The skewed facets of “Juggernaut With Plume for P. Neruda” (1975), with its moody rusts and earthen tones over an ashen ground, is punctuated by a small flash of brilliant color, which appears like a sudden, sharp recollection. While the title evokes a preferred political stance of the post-Vietnam era, the image reminded me of Joan Baez’s “Diamonds and Rust” – an inescapable hit in 1975. We both know what memories can bring; rarely is it politics.

In the 1970s, the decade of muscle cars, painting was another macho performance vehicle. Of these early collages, the artist himself said he wanted the impact “of a truck, not a mini.” Minis they are not, but Chevy El Caminos or Pontiac GTOs are another matter. Hugh Davies, writing in 1979, referred to them as “a wall of machinery in flat-out operation.”

It was an apt analogy for aggressive works built from component parts, moving together like pistons. Besides, the artist’s hot-rodding paint application is of a piece with the era of Stingrays and Firebirds. Heavy, moving machines impel you out of the way. These collages have a similar effect: You have to keep backing up to enjoy them.

Seen from a distance, Mr. Walker’s transparencies are magical, but the closer you get, the more the means – gel in great swaths – asserts itself. Compare the transparencies of Matisse or Diebenkorn, which rely on the properties of pigment, not plastic transparentizers.

Followers of art-world Kremlinology will note Dore Ashton’s swipe in her catalog essay at “conservative critics” who “breathed a sigh of relief when Mr. Walker produced identifiable landscape elements.” She adds, ” But I think they missed the point.” This is a gratuitous reference to Hilton Kramer’s stated admiration, in 2001, for Mr. Walker’s landscapes of the Maine seacoast.

Perhaps Ms. Ashton has missed the point. Mr. Kramer aligned Mr. Walker’s Maine motifs with those by Marsden Hartley and John Marin precisely because they avoided scenic cliches. But abstraction generates its own cliches, and it is these that overtake Mr. Walker’s 2003-04 collages, which are installed in the smaller gallery.

Recent works are art department potboilers of throwaway gestures in raw red, white, and blue. It is as if the artist has begun to mimic his own imitators. Gone are Mr. Walker’s previous tonal subtleties and near-musical subordination of detail to patterned relationships.

One untitled collage refers to the Maine landscape with a smear of real local mud, a hokey literalism that mocks the mastery of analogy on which great art rests. Mr. Walker’s earlier loamy neutrals were wondrously suggestive; mud is just mud. (Try to imagine Haydn composing “The Creation” using real farmyard animals.)

Then there are those illegible scrawls of handwriting, gravely termed “signage” by Ms. Ashton. What Magritte wittily – and fastidiously – introduced in the 1920s and 1930s has dissolved into inchoate decoration. No longer a germinal idea, it has become a platitude that a generation of artists has fallen for like ninepins.

My favorite works here are two very small collages from the 1970s and a series of four spare, schematic drawings: white chalk on a black ground. No bombast, much tremolo. Here are testaments to what refinement of conception and execution John Walker is capable.

Until March 19 (19 E. 70 Street, 212-794-0550). Prices: $18,000-$125,000.