ANDREW ROBISON, curator of prints and drawings at the National Gallery of Art, and a collector of prints himself, beat the bushes for the exhibit of "Master Prints from Washington Private Collections." It opens at the Gallery on Sunday.

Many of the prints he learned of only by word of mouth. Collectors often like to remain anonymous -- especially when the security of a Rembrandt is at stake.

In all, Robison bagged 90 prints from 54 collectors -- and this collection of trophies, he says, rivals any similar show the National has put on from its own stores.

Shall we begin with No. 1 in the catalogue, Picasso's "The Frugal Repast"? Robison calls it "the finest impression in the world of his first print." It is a wonder in greenish ink.

Although it's hard to say which of all Durer prints is his best, "Melancholia," one of several in the show, just may be the one.

An extremely rare G,ericault lithograph, "The Boxers," is among the loans. As is a Pissarro "Twilight With Haystacks," one of eight Degas printed for him. And Manet's "The Balloon," which exists only in proofs (as few as five), because his publisher thought it too wild.

"You can go down the list," says Robison. "How extraordinarily rare these are."

When there are 12 or fewer prints in existence, the labels say so. (They say so, often.) But even if 500 prints survive, as in the case of Rembrandt's "Christ Preaching," there may only be a couple dozen with a quality of impression equal to the one in this show.

A few decades ago, print collecting in Washington was basically confined to Duncan Phillips, Mrs. Robert Woods Bliss and a Virginia lawyer named Frank B. Bristow. But it has greatly advanced within the past 20 years -- the life span of the Washington Print Club, a boon to collectors. (A recent survey of its membership showed that only 60 percent actually owned anything.)

As can be seen in the exhibit, their tastes run from Agostino Carracci to Richard Estes, and everything in between -- such as Goya, Daumier, Whistler, Toulouse-Lautrec, Homer, Bonnard. The show actually surveys printmaking from the 15th century on.

Robison tried to include as many collectors as possible, too. (Senator and Mrs. Claiborne Pell and Ambassador and Mrs. Alan Gottlieb of Canada are among them.)

He describes an impassioned local society of collectors. Almost none of the prints, says Robison, have been inherited. "This correlates with Washington as a meritocracy, a self-made people," he says. "It's a personal commitment -- not, well, this stuff has been hanging around from my grandfather."

For collectors, he says, "the initial desire is to see beautiful things, have beautiful things and to live with them privately."

Then a mania may stir: "You buy one or two, hang them on your wall, and the breakaway point is when your wall is full, with objects that you don't want to let go. For a while you can put them in the closet, rotate them," says Robison.

"Inevitably you face the question of either stopping with walls and closets or making the transition to (storing them in) boxes -- map cases and so forth. That's always a moment of intensity in a collector's life -- to be a little museum," says Robison, who sets the magic number at 50 prints.

"Surprisingly," he says, "in Washington there are at least half a dozen or more who have crossed over that point." MASTER PRINTS FROM WASHINGTON PRIVATE COLLECTIONS -- Opening Sunday at the National Gallery of Art, through March 3.