Prudent visitors to the National Gallery's West Building will take "The Prints of Lucas van Leyden and his Contemporaries" and "Night Prints" in two bites, with at least a lunch break. The best way is to start with Lucas.

The two new exhibitions amount to hundreds of works, at least half of them worth stealing to study at home. The gallery guards are vigilant, however, so be ruthless: March sturdily past the walls and kiss off as many prints as possible; the remainder will eat up more time than there is.

Lucas died in 1533, and while his birthdate is unknown he could have been productive for about 25 years at most. During his life and since he could be compared with only a handful of immortals -- Durer among them. His contemporaries in the Low Countries, generously represented in this show of 140 works, trailed valiantly but generally fruitlessly in his dust.

Not only does the show embrace his work from early to late, it includes a number of impressions of the same plate, showing how time and second thoughts yielded very different results.

Most curious perhaps is that his prints, which art historians divide into early, middle and late periods, don't mature so much as simply change. As his mastery of the medium grows, the power and vigor seem to fade, but the work remains splendid -- whenever it was done. Except sometimes, which is why it takes so damn long to get out of the gallery.

"Night Prints" is nothing like so troublesome. One cannot pass up any of these prints, in which the artists reversed the normal technique, from black on white to white on black, so as to deal with night scenes. Most of them are wonderful, and the rest have to be looked at carefully to see just how good the best are. And there's a hundred of them all told.

Not a few are also funny, especially the section on "Dalliance, Love and Lust." The caption of Daumier's 1880 lithograph of two middle-aged voyeurs peering out a window with a telescope is, "Oh Absolutely! The Big One Is Taking Off Her Corset and the Little One Is Looking for a Flea."

Rembrandt's 1641 etching, "Woman at a Door Hutch," is only playing-card size, yet as the viewer's eyes adjust to the darkness surrounding the candle-lit doorway, the foreground fills with children. A whole afternoon could be lost in M.C. Escher's 1947 woodcut, "Another World."

"Counsel," an 1898 etching and aquatint from "The Weavers Rebellion" by Kathe Kollwitz, seems simple and straightforward until one looks at it again; "Fireworks at the Bois de Boulogne, July 14, 1881," seems to be a fine lithograph -- but it's a great wood engraving.

These folks, spanning four centuries, don't just fool the eye, they fool the mind, and trigger the heart. LUCAS VAN LEYDEN and NIGHT PRINTS -- Through August 14 at the National Gallery of Art's West Building. Open 10 to 5 Monday through Saturday, noon to 9 Sunday. From June 13 through Labor Day, daily noon to 9.