CARICATURES BY PAOLO GARRETTO -- At the Inglett-Watson Gallery, 925 1/2 F Street, NW, through November 15, Monday through Saturday, noon to 6; UNSUCCESSFUL PRESIDENTIAL CANDIDATES -- At the National Portrait Gallery, Eighth and F Streets NW, through November 9.

Italian caricaturist Paolo Garretto knows where to draw the line. He has gone through several styles in half a century, and in and out of style several times, but the bright bold line has always been his signature.

Garretto has outlived many of his subjects -- and critics -- and continues to march, as shown by the recent works in the exhibition at the Inglett-Watson gallery on F Street. He has been no more successful than anyone else in capturing Carter, but his Reagan is righteous and his Anderson just.

The quality and span of Garretto's work tax the memory -- "Who was that fellow ?" -- New Yorker, Vanity Fair, Fortune and Harper's Bazaar as well as from a score of European magazines.

By happy coincidence the Gallery Place Metro station is equally convenient to an exhibit of this century's presidential also-rans at the National Portrait Gallery. The show is small and offhand but worth stopping by on the way back from Inglett-Watson. Gene Debs, Charles Evans Hughes, Henry Wallace, Bob LaFollete. . . What kind of country would they have made us?

Just around the corner from the exhibit in Room 203 hangs a 1968 Norman Rockwell portrait of Nixon that is far and and away the best ever done: It shows both the Nixon Nixon wanted us to see and the Nixon we knew was there. s