It is by a conspicuous coincidence that a show devoted to Jasper Johns's paintings of ''The Seasons'' should be on view through March 7 at the Leo Castelli Gallery, 420 West Broadway, while simultaneously there can be seen in the new Lila Acheson Wallace wing at the Metropolitan Museum what may well be the single largest work of contemporary art ever to be mounted in a great American museum.
It is by a conspicuous coincidence that a show devoted to Jasper Johns's paintings of ''The Seasons'' should be on view through March 7 at the Leo Castelli Gallery, 420 West Broadway, while simultaneously there can be seen in the new Lila Acheson Wallace wing at the Metropolitan Museum what may well be the single largest work of contemporary art ever to be mounted in a great American museum. The work in question is ''1/4 Mile or 2 Furlong Piece'' by Robert Rauschenberg, who rather more than 30 years ago was jointly responsible with Jasper Johns for a historic shift in the ambitions of art. Quite apart from that coincidence, major early paintings by both Rauschenberg and Johns can be seen through March 7 in Part 1 of Leo Castelli's 30th-anniversary show at 142 Greene Street. Quite clearly, therefore, this is a good moment at which to look back at careers that have left a permanent mark upon the history of 20th-century art.
When Jasper Johns and Robert Rauschenberg first came before the public in the mid-1950's, they were widely regarded as vandals, saboteurs and wreckers. When faced with Johns's flags and targets, one well-known New York abstract artist said, ''If that's painting, I might as well give up.'' And when Rauschenberg painted directly onto his own narrow bed and hung it up on the wall, you would have thought from the rumpus that he had violated some kind of loyalty oath. Who were these two, anyway, to dump on the American art scene just as it was beginning to be acclaimed the world over?
But then, with time, it became clear that far from being an act of frivolity that verged on a Federal offense, Johns's ''Flags'' had brought back into painting a sensuous delicacy of touch that had had few equals since Georges Seurat was painting on cigar boxes in the 1880's. It also became clear that far from aiming to create an ephemeral sensation, he was a partisan of the long, solitary, hermetic haul. His paintings were about multiplicities of meaning, rather than about their ostensible subjects, and it was his ambition, as far as possible, to banish himself from them. (In 1971 he said in an interview that ''I have attempted to develop my thinking in a way that the work done is not me.'') Already in 1955, a close look would have disposed of the notion that Johns and Rauschenberg were virtually interchangeable newcomers, bent primarily on outrage. Johns's work was about paradox and introspection. Rauschenberg wanted, on the contrary, to reach out to the whole world and welcome it into his work. (In 1961 he said that ''there is no reason not to consider the world as one gigantic painting.'') Then as now, they both seemed to a foreign observer to be deeply, unalterably American. When Johns drew a penetrating poetry of his own from a light bulb, a drawer, a beer can, a wire coathanger, the numbers from 0 through 9 and the alphabet from A through Z, the result had philosophical overtones, but it also had echoes of the plain speaking and plain dealing that John Frederick Peto, for one, had brought to the painting of common objects in the 19th century. In his ''combine paintings,'' in which found objects and readymade images of every imaginable kind were combined with passages of pure painting, Rauschenberg dealt with the poetics of metropolitan glut in much the same way that Charles Ives in his Fourth Symphony had dealt with the manifold sound structure of New England in an era when music came live, and raw, and unamplified.As time went by, their differences became ever more marked. Johns developed a complicated code system that often seemed intended to cover his tracks. But, when cracked in however small a degree, that system could have a universal poignancy. As Johns is well known to be a close reader of Hart Crane, we have no trouble relating the outstretched hand and elongated arm that have long been a part of that system to Crane's suicide by drowning. Equally well, many other seemingly cryptic images in Johns's work relate to poetry, to older art and to private perturbations. Though for years turned away at the front door of Johns's work, autobiography soon found a way in at the back - so much so, that in recent years Johns has developed into one of the great American soliloquists