On the street level of his store, David A. Gartler offers contemporary posters, books, postcards, artist-designed jewelry and, as he puts it, ''other products reflecting an artist's work.'' But more surprising merchandise is also available. Vintage posters seen there recently included a Biscuit Pernot advertisement from about 1900 for $2,800 and a huge Philips ad for $1,900. Stairs lead down to a lower level, where Gartler stocks collectible original posters from roughly 1870 to 1970, most of them created for advertisers.
Among the selection are pieces by unknown artists as well as posters by Toulouse-Lautrec, Picasso, Chagall, Keith Haring and Andy Warhol. There are also military, travel and circus posters. Gartler, who buys mostly at auctions and from estates, sometimes singles out a poster he thinks is worth reprinting and has it reproduced in large numbers to sell in the upstairs shop.