Whistler's greatness as a painter may still be questioned, but there can be no doubt whatever that he achieved greatness through his prints. Only Rembrandt and Goya surpassed him in etching, and some of his lithographs easily rank among the very finest produced in that medium.
For proof, I recommend a visit to a two-part exhibition of Whistler's prints currently on view here at the Metropolitan Museum of Art. It is large (150 etchings and 75 lithographs), traces the evolution from his very first attempts at printmaking to the delicate drypoint ''sketches in copper'' done up to a year or two before his death, and includes more superb and rare impressions of his prints than I have ever before seen in one place.
''The Etchings of James McNeill Whistler'' was selected and organized by Dr. Katharine Lochnan for the Art Gallery of Ontario. She worked closely with the Met in this matter, and she was also responsible for the excellent book that accompanies the exhibition. ''The Lithographs of James McNeill Whistler: The Gift of Paul F. Walter'' was assembled by David W. Kiehl, and has as its nucleus the 31 lithographs recently given to the museum.
Outstanding among the etchings are prints from the famous ''French'' and ''Thames'' sets, from the first and second ''Venice'' sets, and his late etchings of London, Brussels, Amsterdam, and Paris.
Among the lithographs, I was especially taken by those at Luxembourg Gardens in Paris, at fancier buildings in London, and his informally posed nude models. But best of all is ''Siesta,'' a small, freely executed study of his wife, Beatrice, made just before her death.
This seemingly fragile, casual, and minor work demands a considerable degree of viewer compliance, however, before it will yield up its secrets - and even then, the viewer must not expect anything dramatic. Everything is subtly hinted at and underplayed.
But then that kind of sensitivity was probably Whistler's most distinguishing characteristic as an artist. We see it in every one of his prints, from the way he dominated or caressed a plate to the care with which he wiped his plates to achieve maximum bite or subtlety.
I cannot recommend this exhibition highly enough. Not only does it include a number of the very best etchings ever made, it also makes it possible for those who haven't paid particular attention to Whistler's lithographs to discover how superb many of them are.
This beautiful and absolutely first-rate show will remain on view at the Met through Nov. 11. It will then travel to the Art Gallery of Ontario in Toronto, opening there on Nov. 24, and closing on Jan. 13, 1985.