THE MERCHANTS OF PENNSYLVANIA AVENUE through April at PADC Exhibit Center, Willard Hotel, 14th and F Streets NW.

Washington's small craftsmen and merchants are an endangered species, rather like our real landmarks, such as the Willard Hotel.

Sidney Tabak takes pictures of the dwindling number of people whose days are spent in small shops, and, not by coincidence, his pictures are being shown now at the Pennsylvania Avenue Development Corporation's gallery in the Willard.

Tabak found his subjects by wandering around and stopping in wherever he found a shop whose windows offered an intriguing display or the services of an art that may be dying. His people are humble, dignified and proud of their work, he says, and they stand out in a city dominated by ego and power and our impersonal systems. Some are wealthy, others not. But they may all soon be extinct because urban change has not supported those who specialize in the supplying of live poultry, fresh fruits and vegetables, or in such fine crafts as watch repair.

"I spent several hours or even days at each place before I took any pictures," said Tabak, who believes that using a tripod gave him credibility as a photographer. "It required a level of cooperation because my presence was obvious. These are not candid shots."

Posed yet unpretentious, these are portraits of people at work. Tabak found that shutting off the fluorescent lights helped to dramatize his subjects.

An engraver at her machine, lit by a skylight; a pale-faced tailor peering up with haunting eyes, glasses down his nose and tape measure around his neck; and, shown here, the proprieter of Al's Magic Shop, a long-time hangout for area magicians, gentle and smiling in front of rows and rows of gory and grotesque Frankenstein, Dracula, Wolfman and deathskull masks.