In 1891 Montgomery Schuyler, America's first professional critic of architecture, noted that "the real radical defect of modern architecture in general . . . is the estrangement between architecture and building -- between the poetry and the prose of the art of building, which can never be disjoined without injury to both."

Lewis Mumford commented in 1952 that this "was true in Montgomery Schuyler's time; and it still holds." If anything, Schuyler's observation is even truer today. We are witnessing a healthy, lively debate about the appropriate purposes and styles of architecture. At its worst this debate involves superficial changes; at its best it concerns the whole fabric of our cities, towns and neighborhoods.

This is why, of all the Reagan administration's program cuts and eliminations in the proposed budget for fiscal 1983, none is more picayune or foolhardy than the Interior Department's idea of terminating its financial support for key national and state historic preservation programs.

The historic-preservation movement plays an important part in the crucial debate about the built environment . . . the one most of us live in most of the time. The movement represents the first widespread popular outcry against the manifest disregard of modern architects and builders for the existing physical evidence of the past.

More importantly, the preservation movement itself has for some time been engaged in its own lively internal debate, shifting from piecemeal to environmental preservation -- from the part to the whole, the landmark to the street and, perhaps, from the pure to the impure, the unrealistic to the feasible.

There are, of course, preservationists who persist in the belief that nothing new in architecture is good, as there are developers and architects who still passionately believe the opposite. But the middle is the interesting ground these days, and the possibilities of the moment are immense.

The National Trust for Historic Preservation has become a bellwether of changing attitudes in the historic-preservation movement. Its Main Street Center stimulates thoughtful, economically feasible reconstitution of downtown districts. Its new Inner City Ventures Fund -- an imaginative blend of public and private financing -- is an attempt to encourage preservation of neighborhoods in the areas that need it most. With increasing sophistication, its staff eases troubled local waters where preservation and economics collide.

Michael Ainslie, president of the National Trust, has initiated a counterattack, charging that the administration "is shattering the future of our heritage." Yesterday, he even managed to sneak in a good word for preservation after reading the Gettysburg address in the Lincoln birthday ceremony at the Lincoln Memorial.

To protest was Ainslie's duty. Eliminating these uncostly programs -- at stake is a total of about $25 million -- promises to do great damage to an imperfect but carefully crafted mosaic of federal, state and local preservation programs, and to undo countless private preservation efforts as well.

Specifically, what Watt proposes to jettison are the department's contribution to the operating budget of the National Trust ($4.4 million in fiscal 1982, representing about a third of the total budget) and federal matching grants to the state historic preservation offices ($21 million in fiscal year 1982, adopted by Congress in the face of Watt's "zero funding" request).

The administration's familiar refrain that the states themselves will pick up the pieces is, as Ainslie avows, "highly questionable" given that the highest density of need is in the already financially strained states of the Northeast, South and Midwest. Furthermore, as he points out with reason on his side, there is a tremendous inconsistency in the policy.

The state preservation agencies do the bulk of the early certification work for the National Register of Historic Places, an inventory of built resources upon which the whole federal-state system of preservation relies. The states also are targeted to do most of the certification work necessary to implement the preservation tax incentives adopted last year by Congress.

Watt himself called these tax incentives "the cornerstone of the administration's nationwide preservation program," but his budget proposal fails to consider what will happen to this enlightened program if the state agencies aren't around to do the fundamental legwork for it or if, as would be within their rights, the states simply refused to do federal work for which they were not being paid.

What is likely to happen, in Ainslie's view, is that "the chaos that will ensue will just be unbelievable." Indeed, the mean muddleheadedness of the administration's stance is hard to believe and, ironically, it is this that gives Ainslie and other preservationists heart for the coming struggle. "Frankly," he says, "that's what it took to get the appropriations passed last year and this year the mayors and the developers will force a change" in the administration's plan.

Still, Ainslie's optimism about the outcome doesn't make a clumsy policy less clumsy. The diversion of energies required to fight the budget battle is alone cause for outrage. The idea of having to do it year by year is depressing, for there is no question that the attack upon the painstakingly built structure of historic preservation could not have come at a more inopportune time.

With a little help from friendly developers, planners, architects and builders, preservation can help to provide the means by which the poetry and the prose of architecture can be reunited in our cities and towns. For the feds to leave the game at this fascinating juncture makes no good sense.