Once upon a time, we wore our hearts on our sleeves; now we wear our souls on our T-shirts.

"You pick a T-shirt to tell people who you are and where you're coming from," said one of the staffers who were busy yesterday afternoon setting up the "National T-Shirt Art" exhibit at the Local 1734 Art Collective and Gallery on Connecticut Avenue. "It's like putting on a label for people who need to deal with labels," said another. "A T-shirt can be the beginning of getting to know someone -- like asking, 'What's your sign?'"

"Robin Hood Was Right," said a T-shirt "Every Mother Is a Working Woman," said another. A third joined the conversation with "No More Imperialist War."

At a party held last night to celebrate the opening, about 100 T-shirted guests milled about admiring the T-shirts, some of which were displayed on mannequins (without wigs) while others merely had wire coat hangers. Peter McCall, a Washington writer, wore a Richard Nixon T-shirt. Perhaps because of the subject matter, he also wore a regular shirt over it, buttoned right up to the collar with a jacket and tie. invitations to the party suggested that guests wear T-shirts, but they didn't say anything about having to show them. "Come on, take it off," urged his wife, Celeste, who is also a writer and was wearing a T-shirt decorated with the Hags, a group of women musicians who specialize in Irish music. He unbuttoned slowly, to reveal (over his heart) a small colored picture of Nixon in front of a public building. "He looks like he's levitating, doesn't he?" said McCall -- and indeed the ex-president did look as if his feet were not touching the ground. "It looks like a postcard," McCall added, "because that's what it was."

Technology has now made it possible to put almost anything on a T-shirt, and guests at the party had done just that. "Is that a silk-screen?" Celeste McCall asked Ruth Stenstrom, a member of the women artists' cooperative that runs the gallery. "No," said Stenstrom. That's why it's so faded."

"Susu bilong mama em i nambawan kaikai bilong pinkinini," said a T-shirt worn by Hank Prensky. For those whose pidgin English is not fluent, he translated: "Mother's milk is the best food for the children." He claimed that his shirt, which was published in Papua, New Guinea, in 1977, was the one that had traveled farthest to get to the party, and nobody seemed willing to challenge him.

Perhaps the most striking T-shirts on display were those of Kathryn Konkle, a technical illustrator who draws machine parts for a living and designs clothes in her spare time. These shirts were decorated with found objects sewn onto them -- mostly electronic parts taken from such sources as calculators and clocks. "They are not machine-washable," Konkle warned a prospective customer. "I went a lot of trouble putting in labels that say 'Hand wash -- lay flat to dry.' I hope people notice them."

A more traditional artist (within the non-traditional T-shirt medium) is Saiyda Stone, who runs silk screens in her cellar and distributes a catalogue of 11 T-shirts with themes that range from solar power and "no nukes" to astrological motifs. Jon Huls, another T-shirt designer, does not do it as a business but as a volunteer service for organizations that cannot afford to buy art work -- environmental groups and such political organizations as the Venceremos Brigade.

Once upon a time, clothing was something to protect you from the elements -- or perhaps the laws against indecent exposure. A T-shirt would carry no decoration more elaborate than a few stripes.

Then the T-shirt got glamor. Marlon Brando immortalized the torn T-shirt in "A Streetcar Named Desire." Jean Seberg wore an International Herald Tribune T-shirt in "Breathless" and Sophia Loren probably topped them both when she appeared in a wet T-shirt. Now we have moved into an age when every Gucci bag must scream its name to passers-by, when Renaults have "Le Car" blazoned on their flanks like a coat of arms. And clothing is no longer clothing but a manifesto. Or, occasionally, a work of art.

A few of the 100-plus T-shirts at Local 1734 (whose number is its street address) are works of art. Notable are the hand-painted works of Lee Ella Shipman-Strong -- a lily pad, a woman dancing, a woman's face. There are also embroidered T-shirts. A few bear meticulously crafted lithographs of notable Washington homes -- No. 1 Logan Circle, for example, or the Blaine Mansion on Massachusetts Avenue. But most of them are the work of people who see the T-shirt as a way of improving the world -- warning people about radioactive waste, urging them to drive bicycles, stay out of El Salvador or patronize various rock bands, museums and health-food restaurants.

Some of them have a saving sense of humor or wistfulness. "Take an Artist to Lunch," one pleads, and another, which shows a cat saying "Woof," may be a commentary on liberation movements. Most are dead-serious with only the tiniest trace of humor ("Capitalism Is Organized Crime," for example), but some charmingly parody the style of their neighbors. "U.S. Out of North America," demands one, while another advertises its owner in health-food terms: "This Body Is All Natural. It Contains No Artificial Preservatives, Additives, Coloring or Flavoring." c

Over in Georgetown, a mile or two away from socially aware Dupont Circle, the T-shirts bear, on the whole, more frivolous messages -- often tinged with a Georgetownish sort of flippant angst. "Have a Nice Day Before Some Bastard Louses It Up," urges a typical T-shirt slogan offered for $5.50 by a sidewalk vendor outside Au Pied de Cochon on Wisconsin Avenue.

T-shirts are now in season, but it is apparently a volatile business. Asked how many he sells in an average day, the vendor estimated "anywhere between 50 and 600," paused a moment and revised his estimate: "No, maybe double that." The biggest sellers at the moment have pictures on them as well as words, though the pictures are not in a class with the work of Lee Ella Shipman-Strong. One shows two pandas failing to achieve rapport, with a slogan in Oriental-looking letters: "Only in China." The other, subtly feminist in overtone, has a picture of a kitten and the slogan, "The Better I Get to Know Men . . . The More I Like My Cat." For a while, the best seller was one labeled "Immoral Minority." Less trendy now, it is still available, as is a more wordy proclamation that "Moral Majority Is Neither."

During World War II, the T-shirt was only a part of the regulation clothing issued to U.S. sailors. Since then, it has evolved into a primary means of wish-fulfillment, self-assertion and image-enhancement. A new line of pictorial T-shirts, called Body Language, has no words at all, just pictures of appealing portions of the feminine anatomy.

People use the T-shirt to proclaim their virtues ("I May Not Be Perfect, but Parts of Me Are Very Nice"), to summarize their existential dilemmas ("Toto, I Have a Feeling That We Are Not in Kansas"), to decorate themselves with the emblems of the cars (Rolls Royce, Ferrari, Jaguar, Peugeot, Mercedes Benz) that they drive or dream of driving, and to proclaim their regional loyalties ("I'm Not a Tourist, I Live Here").

Some T-shirts sum up a whole philosophy of life in a few words: "I Have Abandoned My Search for Reality and Am Now Looking for a Good Fantasy." Or: "When God Made Man, She Was Only Joking." Professional identity is a prime subject for T-shirt literature. Washington, being a city of lawyers, has many T-shirts that relate to the legal profession: "Lawyers Do It in Their Briefs"; "Attorneys Make Better Motions"; "Old Lawyers Never Die; They Just Lose Their Appeal."

But whatever their overt content -- political, philosophical, artistic or anarchistic -- a majority of T-shirts seem to have as their subtext a message that is printed openly on some: "Single and Looking to Mingle."