The 104 photographs -- all portraits, all polite--that go on view today at the Kathleen Ewing Gallery, 3243 P St. NW, are not themselves for sale. They are there as advertisements for pictures yet unmade. The viewer is invited to use this exhibition as he might a mirror. Do I wish to look serene or senatorial, familial, romantic, learned or profound? What pose might I strike, on what set, in what lighting, to show me at my best? This exhibit offers answers. "The idea," says Allen Appel, who picked the 41 artists in it, "is 'Picture Yourself Here.' "

All of them are ready to do portraits on commission--for $50 or $100, or in the case of David Hume Kennerly, for $1,500. If you must have a portrait for your yearbook or your boardroom, for the jacket of your novel or to appease your mama, this is a place to shop.

Formal portraiture, these artists know, is a tricky business. Because the sitter tends to greet the first view of his portrait as he would the sound of his recorded voice--do I really look that fat?--much tact is required. Flattery is useful. Brutality is out. No wonder J.S. Sargent, who charged his sitters plenty, once defined the portrait as "a painting with a little something wrong around the mouth."

Appel and Ewing offer three more definitions. The first--"A portrait is a picture of a person"--is from the 19th century; the second--"A portrait is a picture of a person who knows he is being photographed"--is from Richard Avedon. The third, which they devised themselves--"A portrait is a picture of a person who knows he is being photographed and desires to be photographed"--applies to all the photos in their curious, touching show.

Their styles vary greatly, but most of them suggest a sort of awkward compromise, a peace struck between egos. Joe of Joe's Tattoo Shoppe, in Don Fear's telling portrait, seems to be a toughie--he is posing in his leathers with his Harley and black dog--but his toughness seems veneer. His delicacy is revealed in the way he spells "shop." Fear's charge for a sitting is $75.

Art Stein's campaign shot of Sen. John Warner (R-Va.), a Superman in pin stripes, is a picture without humor. But politicians' portraits--there is a grand one here, in perfect living color, made by Arnold Kramer of Sen. John Glenn (D-Ohio)--are not meant to be funny. Stein charges $125 for a one-hour sitting; Kramer's portrait fee is $500. A portrait somewhat cuter, but equally conventional, is Kennerly's of TV's Kate Jackson. She wears a large straw hat and has a flower in her mouth.

A number of these artists--Appel, Kramer, Paul Feinberg, Joyce Tenneson, and W.E. Butler--are highly skilled professionals. But their art form, though familiar, is usually neglected. We want to see the bride, not the style of the artist who was paid to take her picture. Appel notes quite rightly that museums rarely offer pictures of the sort included in this show.

A number of the best--by Joan Giesecke ($200), Barbara Hadley ($125), Reed Isbell Meek ($100), Claudia Smigrod ($175)--are portraits of small children, who, although at ease, never snarl or howl.

These artists do have styles. Appel's pictures are hand-colored and tend to look like paintings, though his portrait of dealer Harry Lunn looks more like a sculpture, "Balzac" by Rodin. Tenneson's portraits are as soft as pencil drawings. Mary Paul Taylor ($240) poses all her subjects before the same rough wall. Allan Janus makes small ambrotypes (and charges $75), Tom Shuler prefers platinum prints (and asks $750 for a set of four). A number of these artists, finding single images inadequate, offer sequences instead. Smigrod's 12-shot sequence of a little girl with a balloon says far more than one picture could. So, too, does Fear's two-picture portrait of an aging couple on a beach. In the first the thoughtful husband adjusts his wife's collar; in the second he prepares himself for the portrait that will come, and his dignity is piercing. Kramer's work is tougher, Appel's more adventurous, and Butler's more professional, but if it's sweetness that you want, you might consider Fear.

The sitters here are old and young, pompous, unpretentious, beautiful and plain. They pose singly, in couples, as families, or even as American Legion groups. They are sometimes shown with props. (The post cards that we see tacked up behind Joe Shannon, the Washington painter, in Mary Swift's good photo provide a portrait of his taste.)

Though void of nudes and street bums, and of portrait shots that shock, Appel's exhibition is deeply democratic. He tried to find a portraitist for almost every taste, and came close to succeeding. He is among the most intelligent artists in this city. His show says more, much more, about the ways we see ourselves than do most exhibits given to photographs-as-art.

"Reflections: Personal Visions in Portraiture: An Exhibition of Washington Photographers Currently Accepting Commissions" will run through July.