"That isn't one of the paintings you did under the WPA, is it?" Washington artist Jacob Kainen was asked yesterday as he stood near one of his works in the National Museum of American Art. "No, this is 197 . . ." hhe began, but Karel Yasko interrupted.

"Listen," the GSA's rescuer of endangered WPA art said, "artists like Kainen wouldn't have developed if they hadn't eaten."

Yasko has spent the last 10 years or so wresting New Deal-era art literally out from under the wrecker's ball in public buildings, or finding them hidden away in closets and basements. He was one of the museum's hosts yesterday evening at a reception sponsored by WETA to give some New Deal old-timers a taste of "New Deal for Artists," a WETA-promoted 90-minute TV special tomorrow evening on Franklin Roosevelt's (and Harry Hopkins') Public Works Arts Project.

Described in the special as the biggest public patronage of the arts since the Renaissance, the PWAP, of course, meant writers, actors, musicians and photographers as well as artists like Kainen and Ben Shahn (who was also a photographer) and Joe Stella. It meant Harlem's Lafayette Theater and the "Negro Unit" of the Federal Theatre Project, where John Houseman and a 19-year-old Orson Welles produced a black MacBeth as well as original plays on the American black experience.

At yesterday's pre-screening reception at the museum, Mary Dublin Keyserling, economist and one-time head of the Labor Department's Women's Bureau, said she was "fuming and fussing" over the current state of domestic affairs, a thought echoed by economic consultant Robert R. Nathan. Both Keyserling and Nathan were among the bright young idealists the New Deal attracted. Both had tears in their eyes after watching the half-hour preview of tomorrow's program