The subway is, in the words of one prominent design critic, "hardly a model of Cartesian rationality."

In confusion as in crime, the New York subway system towers above all others. To be lost therein is to experience an existential nightmare, and charting its 230 miles of track is both an esthetic challenge and an awesome public trust. So when the city replaced its map late last month, both urbanologists and art critics were moved to comment.

The old map, unquestionably the most distinctive ever made, was created seven years ago when Massimo Vignelli produced a design that married Peter Max and Piet Mondrian, with Morris Louis thrown in, as best man.

It remains a stunning piece of abstract design, if somewhat less effective as cartography.

Paul Goldberger of The New York Times admired its "rich, almost luscious colors" and called it, "a sillfully drafted exercise in polychromy."

A Manhattan gallery owner talked of its "abstract pattern," its "sinewy color" and its "strong structure."

"It's the embodiment of the whole '60s" concluded Stephen Miller, curator of the Rpints department at the Museum of the City of New York. "On a purely esthetic level, I'd like to eliminate all of the writing and put it up on my wall."

Not surprisingly, Vignelli prefers his design to its successor. "This new map is a tremendous step backwards," he said recently. "It's a return to the Middle Ages by an agrarian mind."

But his map's particular artistic appeal also was its downfall. Critics charged that it inteed belonged in the Museum of Modern Art - anywhere in fact, except in New York's 6,400 subway cars. For all of its beauty, they said, it was a functional disaster.

So it was replaced by the new one - designed by Japanese artist Nobu Siraisi - which is as representational as Vignelli's was abstract. If less attractive, though, it appears to be a good deal more useful.

"The old one was beautiful, but totally nonfunctional," said Ben Blond, whose gallery, Cityana, hosted the public display of one proposed replacement. "What's really important about a map is to know where the hell you are when you get above ground, and the old one was a disaster at that."

"A subway map should tie the real world above ground to the system underground, and Vignelli's simply didn't do that," echoed Dr. Arline Bronzaft, an environmental psychologist involved in the creation of the new one.

Bronzaft ran one test involving the old map in which she sent 20 graduate students from Columbia out into the harsh subway world armed only with the Vignelli map. They were to reach four different points of varying difficulty in the system. "They did really poorly," she said.

Vignelli used 16 different shades of colors to identify the myriad of routes which span the city. He also reduced the maze of tracks to a series of 90 and 45 degree angles. The map consists of geometric lines in space. It is completely schematic; there is no hint of geography to it.

"The beauty was totally accidental," Vignelli explained recently. "And I disagree completely about its functionalism. The entire world uses schematic maps - Berlin, Tokyo, Paris - every major city. London has used them since 1933. They're much easier to grasp."

In the new map, however, the outlines of Manhattan, Brooklyn, the Bronx, Queens and the tip of Staten Island are all clear, contrasted by assorted rivers, bays and bridges. Parks are included, streets are named, and colloquial designations like "China Town" appaer.

By and large, the new map has been well received. The New York Times editorialized favorably about it, and the consensus around town is that it is a more informative document than its predicessor.

But most people acquainted with the Vignelli map already miss the abstract beauty it brought to New York's subterranean world. If it isn't great cartography, it does make wonderful art. CAPTION: Map 1, The old map was visually distinctive; Map 2, The new one was designed to be more helpful. By Donal F. Holway for The Washington Post