Washington's museums, so long loyal to the painting, the drawing and the print, have only recently begun collecting photography in depth. Two new exhibitions of recent acquisitions -- one at the National Portrait Gallery, the other at the Corcoran -- demonstrate abundantly the rightness of that move.

The Portrait Gallery's pictures show the faces of the famous. The frequently antique likenesses of generals, athletes and actors, presidents and poets, were not selected for their beauty, but for the importance of the persons they portray. The pictures at the Corcoran are reflections of the present. Most of them are new, and all were made as works of art.

Though photographs were banned once from the Portrait Gallery's collection, that silly and restrictive law was changed in 1976. These well-selected pictures have an immediacy and accuracy that, at least in our age, most painted portraits lack.

Though most of them are formal, staged or stiffly posed, they are in unexpected ways, eerily enhanced by their affectations. These pictures show us people, but they also tell us much about the fashions and pretensions of our past. John Barrymore as Hamlet glaring at the viewer, Jean Harlow and Clark Gable smooching for the camera, Ted Shawn the daring dancer (he is seen here, nude, in the pose of a Greek archer) and even John Wilkes Booth strutting in his toga, tell us quite as much about the show business of their times as they do about the performers they portray.

The photographs of authors here are equally suggestive. Alice Boughton's Henry James, which could not be more Jamesian, shows the master in a moment of esthetic delectation: He is admiring a painting; his silk top hat is shiny; his cane nicely slender; his gloves soft dove-gray. The writings of Walt Whitman were more vernacular, less formal, and in his portrait here Whitman wears no tie. Here also are Ezra Pound at 28 (by Alvin Langdon Coburn), Emerson in study (a little Gothic bookstand holds his open book) and Marianne Moore with elephants. She much enjoyed the zoo.

Other phots here evoke the modesty of athletes (Babe Ruth with bat on shoulder), the zeal of the abolitionists (Sojurner Truth, for instance), and the pomposities of generals. Gen. Joseph Hooker, in Mathew Brady's photograph, does his best to look like a statue in the park. Though the Civil War uniform of U.S. Grant (photographed by Alexander Gardner in 1865) looks a little baggy, that of Douglas MacArthur, who posed for his picture in August 1930, is impeccably pressed. The partial phoniness of Buffalo Bill, the pride of Teddy Roosevelt and the haughtiness of Frank Lloyd Wright illuminate their portraits. This show in a sense is a discontinuous portrait in our history. There are now 1,200 photographs in the Portrait Gallery's collection, and this delightful show reminds us how much poorer it would be if they were not there.

Goaded by Jan Livingston, the Corcoran of late has committed itself deeply to contemporary photography. (And to this region, too; more than half the pictures here were made by local artists.) Of the 40 images in its recent acquisitions show, almost all were taken in the past two years. Their quality, in general, is admirably high.

One virtue of this show is that it lightly surveys the currently fashionable sytles of art photography. A number of these pictures, those of Margot Kernan, Nancy Rexroth and Tom Kilby, a latter-day Constructivist, flirt with pure abstraction. Others on display, by Ronald Geibert, Neil Maurer and John McIntosh, explore in subtle ways the tradition of the still life. A mood that is disturbing, perhaps even menacing, underlies a number of the better images. In Avery Danziger's "K-9 Dream No. 16," there is a dark dog snarling. One of Robert Epstein's subjects is a herd of just-flayed pigs. Rosalind Solomon has photographed a Guatamalan corpse that is about to be interred with a bottle of Pepsi Cola. The finest portraits here, those by John D. Radcliff and Alex Jamison, also shock a little bit, but in more suble ways. They are blazingly direct; their lack of politesse, the way they seem to break through their subjects' privacies tend to shock the eye.

What seems newest in these pictures is the attention paid to color. It gives life to Kernan's flower studies, McIntosh's tryptich and Richard Rodriguez's moonlit "Chris's Room." What seems oldest in these photographs is the way that some of them pay homage to the famous artists of the past. Tom Zetterstrom's "Black Spruce" owes much to Ansel Adams, Jack Teemer's handsome study of backyards in West Baltimore bows gracefully to Walter Evans and Philip Trager's New York cathedral calls to mind Atget.

The Corcoran photographs were purchased with the aid of funds from the Polaroid Corp. and the National Endowmen for the Arts. They will be on view through March 8. The Portrait Gallery's show will close on April 19.