Twenty or so years ago, Riverdale's Greenbelt was under assault. The city planned to cut down virtually all the trees along the Henry Hudson Parkway. Metro-North proposed driving a road through Riverdale Park to make it easier to reach its tracks. The area's schools and nursing homes were expanding, covering more and more of their campuses with buildings.

A company sought a zoning variance to permit it to buy the Campagna mansion across the street from Wave Hill, pave a parking lot for 40 cars and make the home its corporate headquarters, raising the threat that the remaining 19thcentury mansions overlooking the river would be converted to commercial use.

Developers coveted the property that is now Wallenberg Park, and unveiled plans to denude much of the Delafield Estate west of the parkway and Chapel Farm next door to Fieldston.

In Fieldston itself, new subdivisions were being built, and house-proud residents were replacing some of the neighborhood's older homes with larger ones, or building additions larger than the originals, sacrificing trees, lawns and gardens.

It was in these circumstances that alarmed neighbors founded the preservancy, in order, as its mission statement says, "to protect and preserve the natural beauty and neighborhood character of the Riverdale area through public information, monitoring of development, and long-term planning."

Last week, the preservancy's annual meeting devoted itself to none of these purposes - or so it seemed.

"This was really the year climate made it onto the city agenda," said Riverdalian Stephen Hammer, director of the Urban Energy Project at Columbia University's Center for Energy, Marine Transportation and Public Policy. So Dr. Hammer put climate on the neighborhood agenda by convening a panel discussion devoted chiefly to global warming.