Any exhibition that includes works by Rembrandt, Goya, El Greco, Caravaggio, Rubens, Titian, Bellini, Tintoretto, and Cranach - and yet has as its star attraction a small painting by Memling - cannot be described as an exhibition of absolute masterpieces.
That is precisely the case with ''Old Master Paintings From the Collection of Baron Thyseen-Bornemisza'' on view at the Metropolitan Museum here. Although the baron's collection is considered among the very finest in the world (some would say second in quality only to the royal collection inherited by the Queen of England), the majority of the 59 paintings from it in this show are considerably below first-rate quality.
Those that do stand out - in their own right and not because they bear great names - are Caravaggio's ''Saint Catherine of Alexandria,'' Van Eyck's tiny diptych in grisaille, Van Heemskerck's ''Portrait of a Lady With Spindle and Distaff,'' Hans Baldung Grien's ''Portrait of a Lady,'' the anonymous Nurnberg Master's ''Portrait of a Young Woman,'' Boucher's ''La Toilette,'' Watteau's ''Pierrot Content,'' and of course Memling's breathtaking ''Portrait of a Young Man.''
As to the Rembrandt, well, it's a third-rate example of his work, a portrait whose main distinction is that it is from Rembrandt's hand. Much the same can be said of the portraits by Titian, Tintoretto, and Goya - although the last named does have a certain verve to it. Of the other great names: The Rubens is an embarrassment, the two El Grecos are more manner than art, and the Cranach is of interest mainly for its landscape background.
All of which is not to say that this isn't a very worthwhile exhibition in its own right - only that those intending to visit it should realize that they will not be seeing great examples by great artists. That the best things in it, by and large, are by painters who do not quite rate full first-class status.
It's at the Metropolitan Museum through Dec. 6.