Today's rally to save Lever House is in New York. But Park Avenue's cool glass monument to postwar vitality is a landmark not only in Manhattan but in the art of architecture. No wonder the voices in its behalf range far and wide, with the American Institute of Architects joining neighborhood groups in urging that Lever House not be destroyed.
It could be destroyed, if developers succeed in having the city's Board of Estimate reject designation of Lever House by the Landmarks Preservation Commission. The board is scheduled to vote on the matter next month.
Some might find the loss of the pioneering glass skyscraper (21 stories) more acceptable if its proposed replacement were not a 40-story tower that one architecture critic describes as ''garish.'' But the issue is really whether Lever House is important enough to architectural history to make the question of replacement irrelevant. From this distance it looks as if it is.
Whatever happens, something positive may come from the current flare of controversy. The landmarks commission is being pushed to raise funds and expedite its ongoing survey of New York buildings. If such a survey had been in hand earlier the effort to preserve Lever House would presumably not have come at almost the last minute last fall.
A footnote: The city's landmarks, by statute, must be 30 years old. Lever House gets under the wire at 31. Still young for a landmark. Or is it? A building whose transparent simplicity symbolizes ''modern'' may be hard to think of as a landmark of yesterday. In decades of rapid change the past gets younger all the time. But that's no reason not to honor it.