THE FIGHT TO SAVE New York's Grand Central Terminal has brought a grand triumph for admirers of that station and for historic preservation in general. The victory came in the Supreme Court's recent decision upholding New York City's landmark-preservation law, as used to block Penn Central and a British corporation from building an incongruous office tower over the elegant terminal. The decision should help save other important privately owned structures, too, because the court has established a strong legal foundation for many kinds of landmark-protection laws.

The case was a crucial test of a city's ability to preserve its architectural treasures and historical ambiance. The terminal is a national showpiece of beaux Arts elegance. The skyscraper plans were aesthetic atrocities: one design called for a 55-story concrete tower above the terminal and an alternative involved stripping off the station's facade and encasing its remains in a 53-story box.

The case turned on the basic legal issue that has bedeviled many preservation plans: whether landmark designation, by restricting the uses of a structure of site, amounts to an unconstitutional "taking" of private property without compensation. The court's answer was clear. "We find no merit" in Penn Central's argument, Justice William Brennan wrote. It is "quite simply untenable" to assert that developers must be paid whenever they are "denied the ability to exploit a property interest."

The decision puts landmark laws on much the same legal footing as zoning and other land-use controls. It gives communities considerable power to protect privately owned historic structures - as long as preservation programs are systematic, clearly promote the general welfare and treat property-owners reasonably. For instance, the court stressed that New York allows owners "a reasonable return" from landmark properties, permits them to transfer development rights to nearby sites - and offers tax relief if a landmark ceases to be "economically viable."

Economics, of course, is the real problem in many preservation fights. In this respect, Grand Central Terminal is exceptional because its future as a station does not seem to be in doubt.But landmark laws alone won't save a historic station where the trains no longer stop. And where commerical landmarks have fallen into disuse or disrepair, the cost of rescue missions can be very high. In Chicago, there is no lack of civic appreciation of the early skyscrapers that rrmain: the challenge is finding the means of saving them. Locally developed and preservationists are now debating whether several old downtown buildings are worth saving - and at what cost to whom.

This, too, underscores the basic point that the fate of landmarks is not just a private affair. It involves community decisions on the value of various properties. But preservation also requires a public willingness to bear some costs - whether by foregoing the tax revenues from development or by underwriting, one way or another, significant properties that can no longer survive in the marketplace.