New York City is now home to the most comprehensive, and hence ethnographic, museum in the world. A New Yorker, George Gustave Heye, began the collection in 1896 and later founded the museum. As provided for in its charter, the Museum of the American Indian must remain in the city of New York.

The city's Commission on the Year 2000 recently issued its remarkably candid yet hopeful report, giving it the title New York Ascendant. By the turn of the next century, the report states, New York "should be the unrivaled world city."

I must dissent. New York was the "unrivaled world city" at mid-century. The question concerning the year 2000 is whether it will continue to be.

This is the root of the matter concerning the Museum of the American Indian.

At the beginning of this century New York had assembled the components of its ascendancy. One indispensable component was a civic culture that instinctively understood that a world city is in part defined by the presence of world-class institutions of learning and culture.

This was the civic culture that produced the Heye collection, subsequently given in trust to the Museum of the American Indian.

There were two aspects of this culture. On the one hand there was a monied, somewhat self-designated elite much involved with enriching the city in this regard. From the Morgan Library to the Guggenheim Museum, we see its works all about us.

But there was a second aspect, less visible. This elite prospered in the context of a political system that discreetly deferred to its wishes and facilitated them. It was in the era of Tammany that the city built Central Park, in which we now find The Metropolitan Museum of Art.

This civic culture is faltering. We witnessed strong residual energies in the efforts of James D. Wolfensohn's Custom House Institute, made up of New York citizens who understand that we had a structure of value here that was not to be lost. On the other hand, that culture has failed utterly where the trustees of the museum are concerned. An earlier generation of New Yorkers would have raised the money and built their own building and never for a moment thought to let it leave the city.

Similarly, the political system of the city would have long since seen to it that this was made possible insofar as municipal initiatives were required. Instead we have had not so much indifference as incomprehension.

Ineluctably, greater energies prevail. Already in this decade we have seen the Sackler collection lost by the Metropolitan, spirited away by the Smithsonian. Now the Smithsonian wishes to abscond with the Indian museum as well.

If it does, we will have only ourselves to blame.

Be clear. The offer of the Custom House on Bowling Green in lower Manhattan is good for another 18 months. No more. President Reagan assured us, through David Rockefeller, that the executive branch of the federal government was most willing to have the Custom House made available to the Indian museum. The next president will want the museum on the Mall. I would not be surprised to hear such a commitment made during the course of the presidential campaigns, already begun.

Be clear. If we lose this premier ethnographic collection in the world, the city will die a little. If we lose it only later to realize what it was we lost, it will be clear we were already a bit brain dead. -- Daniel Patrick Moynihan is a Democratic senator from New York. This is adapted from remarks made last month at a hearing on the transfer of the U.S. Custom House in New York to the Museum of the American Indian.