Despite the fact that James Blish was considered a major science fiction stylist and visionary, few outside a hardcore cadre of readers knew him as anything but the man responsible for 22 volumes of Star Trek adaptations by the time he died in 1975.

A quarter-century later, the majority of Blish's work remains out of print, but a beautiful reprint of Cities in Flight (Overlook, $35), one of his most revered works beyond the Starship Enterprise, should help introduce a new generation to the man who opened up SF to the philosophical concerns of "real" literature.

The four linked novels that comprise Cities in Flight share a distinctive and disturbing vision of a far future -- first intimated in the pages of Astounding in 1950 -- in which oppressive government, depleted resources, and the pioneer spirit have loosed the cities of earth to the stars.

Thanks to anti-aging treatments, the denizens of these nomadic cities, called "Okies" after the Oklahoma farm families forced into a migrant lifestyle by the 1930s dustbowl, are nearly immortal, but economic forces still dictate they wander the starlanes in a desperate search for work.

The action spans the centuries, but remains fixed on one of the proudest of the mobile habitats, The City of New York (its motto, proudly emblazoned on City Hall, is "Mow Your Lawn, Lady?") and its immortal mayor, John Amalfi.

On the surface, the first of the four novels, Earthman Come Home, first published in episodic form in 1950, is a straight space opera complete with massive space battles in which dozens of cities burn like moths at a candle in a single sentence.

That said, closer analysis reveals that the novel is at its core an allegory of the Great Depression, complete with a currency failure, vast populations wandering for work and a final march on the center of political power, Earth (a reinvented Washington on a planetary scale) itself.

One planet in particular, ravaged by ecological disaster, drives the point home. Blish lingers over dustbowl scenes, describing haunted farmers in language that explicitly recalls photographs from that era.

This novel is the overture and thematic heart of the series. Through his careful study of his setting, in all its economic, social and political dimensions, Blish has not only created a coherent future history, but grappled with real social issues with an uncompromising focus arguably not seen in mainstream science fiction since H.G. Wells.

They Shall Have Stars, the second movement in Blish's grand space opera, originally appeared in 1957 and reflects the social fabric of its times well.

Set in our own near future, the novel depicts a world in which the West has chosen to combat the Stalinist menace by mirroring its adversary and the FBI, in particular, has become menacingly all-powerful, gripping science and progress in a paranoid bureaucracy.

In short, this is of course an allegory of the McCarthy era, but it hasn't aged well as a work of science fiction. While the story provides background for the other segments of Cities in Flight, it does so almost plotlessly, plodding along as it indicts one human foible after another.

However, as Blish ambles along, he foreshadows two major themes for the novels to come -- the relentless libertarianism that spawns the Okie culture, and the belief that religion is either a con or a method of mobilizing a barbarian horde. In this case, the con men are The Believers, zealots who use special effects and mind-altering drugs to inflict religious epiphanies on hapless passersby.

The barbarian horde shows up in The Triumph of Time, the most metaphysical of the series and, by internal chronology, the furthest in the future. Set several hundred years after Earthman, Come Home, it also plods in spots, but has much plot movement than its immediate predecessor to keep the reader's interest.

Blish anchors the cosmic turmoil with his primary concerns here: the psychology of immortality and the character of John Amalfi, undying mayor of New York.

Faced with both the impending destruction of the universe and an onslaught of fundamentalists, Amalfi outsmarts the former, but even he must succumb to the latter. In a very literal sense, he dies so that the universe might be reborn -- from his own body.

The messianic subtext here is obvious, and it is noteworthy that Blish was one of the first SF writers to incorporate overtly religious themes into his work. His Hugo-winning A Case of Conscience, which appeared the same year as The Triumph of Time (1958), examines a Jesuit missionary's crisis of faith on a world where the natives have neither any concept of original sin nor any major societal problems despite an utterly atheistic ethical system. Heady stuff for a genre normally relegated to realm of adolescent boys.

Lest that sacred core constituency of science fiction be forgotten, A Life for the Stars, Blish's fourth and final visit to the Okie setting, is much lighter in tone than the earlier volumes.

It's a fun adventure tale, complete with a shanghaied young protagonist, kidnapping, daring rescues, narrow escapes, great rewards, and very little subtext. Still, the most haunting image of the entire series emerges here, as Scranton, PA, lifts off from an utterly depleted Earth to seek a Rust Belt somewhere in the interstellar void -- Pittsburgh, it seems, has already claimed Mars.

While Cities in Flight is somewhat uneven and at times denser perhaps than it needs to be -- even at 590 pages -- it is still a must for anyone wishing to truly understand where science fiction first began self-consciously groping toward "literary" structures and concerns.

Its vision is grand, magnificent and wondrous, and has aged surprisingly little in half a century beyond the occasional slide rule left casually on a desk. One can only hope that this book and Del Rey's forthcoming republication of A Case of Conscience will provoke a much-deserved resurgence of interest in Blish's work.