Three years ago, directors of some of the world's top museums, meeting in Munich, commiserated over a major annoyance: the growing demands from countries like Greece and Italy that they return ancient artifacts.

What emerged from the meeting was a defiant statement defending their collecting practices. Signed by the directors of 18 museums - from the Louvre to the Hermitage in Russia to the Metropolitan Museum of Art to the J. Paul Getty Museum in Los Angeles - the document argued that encyclopedic museums have a special mission as treasure houses of world culture, and that today's ethical standards cannot be applied to yesterday's acquisitions. That philosophy is now under siege as never before.

In Rome, a former Getty curator sat tensely and quietly yesterday as her trial began on criminal charges of conspiring to import illegally excavated antiquities for the museum. (Page B8.) On Tuesday, Philippe de Montebello, the longtime director of the Met, is to meet in Rome with a lawyer for the Italian Culture Ministry to discuss works in the museum's collection that the Italians say were looted. Italy is insisting that several other American museums account for dozens of ancient artworks that made their way into their collections.