SOMETIME take an hour out to psychoanalyze the presidents at the National Portrait Gallery.

They're all there on the second floor in big oils, busts and daguerreotypes, and it is fascinating to observe not only the individual faces, but the trends in presidential fashion.

For instance, the earliest ones seem quite aristocratic, men of quiet dignity and old family. Madison is a surprise: a fine old man, somewhat choleric, a born chairman of the board. Jefferson appears at age 76 in a bust, and it is a new view of the man. The youthful beauty is gone but the character remains. Quincy Adams could be the headmaster of Harvard or some other Ivy League school. Very much a founding father.

Washington has a whole room to himself, including a Stuart, a Peale, a Sharples and some engravings that leave you with a pretty strong impression of how the man looked.

With Andrew Jackson you see a change: the rugged, rough-spoken soldier, at the opposite end of the social rainbow from those eastern seaboard patricians (but still a WASP, of course). Then, back to the tidy Van Buren and William Henry Harrison, who campaigned and won as a backwoods fighter but in fact was a sophisticated country squire.

His face and John Tyler's are especially interesting, if only for their unfamiliarity. Tyler is a revelation: yet another southern gentleman, accustomed to having his way, charming but rigid enough to make enemies in both parties. The painting shows him after he held office, and he seems more relaxed. His one great achievement, in case you had to know, was annexing Texas.

You can find superb old photos of Tyler, Jackson and even Quincy Adams, more intimate and revealing than the somewhat complimentary portraits. Though the gallery does show a few original daguerreotypes alongside the paintings, they are almost impossible to see. It would be great to display nice big sharp prints of these tintypes next to the oils, if this could be done without clutter.

Lincoln is represented by several old photos and a dreadful painting based on life sketches by George Healy. It gives Abe the eyes of a movie star.

Gradually, down through the 19th century, you see changes. The paintings seem to get more idealized, more slick. Grant's likeness is terrible, hardly recognizable as the still, steady, intelligent figure of the Mathew Brady photographs, though his wife Julia said he really looked like this during "that sad summer" of Spotsylvania and Cold Harbor. The Bradys and other vintage photo portraits are down the hall in the Meserve Gallery.

More important, the aristos are gone. We see a succession of merchant princes, businessmen, professional pols. (Any time you rebel against our tradition of amateur presidents and wish for a real professional, just think about that brilliant succession of pros: Hayes, Garfield, Arthur, Cleveland and Ben Harrison.) Most are heavily bearded, which makes them appear pompous, though McKinley achieves this effect cleanshaven.

Teddy Roosevelt gets a bronze relief that reveals his vitality, his beautifully shaped head, his sexy neck. Some of the modern portraits are even more, one might say, romantic. Taft's massive presence is shown but not his intelligence. Coolidge is inescapably Coolidge. Franklin Roosevelt, depicted at Yalta, of all times, hardly looks his best, and artist Chandor has given him eyelashes worthy of Twiggy. Harry Truman's famously bright eyes are dull here, and a petulant Kennedy gets a curious impressionistic visage.

On the other hand, Lyndon Johnson comes through gloriously, haloed by a Capitol sunrise. And Nixon's portrait by Norman Rockwell is easily the best of the modern likenesses. Jamie Wyeth did Carter as an articulate, shrewd farmer, in watercolor. Interesting.

Succinct comments on each president add tremendously to the show. You think you can judge a man by his appearance? See what you make of these guys.