MUSEUMS AREN'T WHAT THEY USED TO BE

Museums throughout the centuries were hallowed repositories of history and culture, bringing the past to new generations with virtually monolithic rules and programs.

Not any more.

In a matter of just a few years, museums worldwide have been undergoing tremendous changes, and at such a rapid pace that their usual staid character and solemnity have been changed for good.

The basic dictionary definition of a museum is ''an institution, building, or room for preserving and exhibiting artistic, historical, or scientific objects.''

And indeed they did, amassing archaeological objects, works of art, documents, and other samples of the past.

But as collections increased and demands grew, the original structures were supplemented by new halls, galleries, and entire wings.

It didn't take long for auditoriums or sculpture gardens to appear, as at the Museum of Modern Art in New York, the Hirschhorn Museum in Washington, the Museum of Modern Art in Fort Lauderdale, Fla., or the Fondation Maeght in Vence, France, among others.

Even faster was the transformation of what were little more than stalls inside the museums, selling postcards and posters, into small shops, then stores, and lately veritable department-store complexes selling art reproductions, jewelry, textiles and clothing.

Modest snack counters became coffee shops, then full-blown gourmet restaurants.

Also, small rooms for lectures and recitals became auditoriums for discussion panels, audiovisual presentations, and film showings, deriving into facilities for courses and seminars, whole departments for art and history classes, and theaters seating hundreds.

At the recent opening of the new San Francisco Museum of Modern Art, the New York Times art critic Michael Kimmelman noted: ''Museums have increasingly become multipurpose emporiums, places to shop and eat. They depend on the income they get from these businesses, and their buildings are designed accordingly.''

New facilities undoubtedly attract a larger public and tourists, says George Passwell, spokesman for New York's Metropolitan Museum of Art.

The latest changes at the Met involved reconstruction of galleries for 19th-century paintings a two-year, $12.5 million effort, including a restaurant.

Last year, the museum drew a record 4.6 million visitors.