Postcards, artful or truly awful, grow sillier but more valuable with age. What with slam dancing and "Love Boat" filling the current quotient for zaniness, it's reassuring to know that the country has progressed from even shallower yucks in the Thirties. "Take a Friend's Advice and Buy One," is the message above a henpecked husband contemplating a muzzle for his overbearing wife. The postmark is Grassy Meadows, West Virginia, November 7, 1908. In the upper right-hand corner on the back, a box holds the quaint instruction: "Place one-cent stamp here." It's an antique postcard, now on sale for $5. They bear old bromides, shameful examples of what passed for jokes in FDR's day. Swimsuited young ladies at the beach and black shoe-shiners are branded with sexist or racist captions, the standard of the day. Here's one: Obese woman rolling up her sleeve, puny man splat on the ground, stars shooting out of his head, their cars accordioned together -- "Always give a woman the right of way . . . especially if she has the right of weigh." A riot? Try this: A curvaceous miss on the lap of a bald, mustached boss beside his desk -- "Hello, employment agency? I got the job!" Hilarious, circa 1910. Union Pacific Railroad's pictorial cards from the Fifties are "I Love Lucy"-style, with couples lounging in the clubcar. The world is long on silly-looking animal cards; monkeys in human wardrobes are abundant. Tinted "Colortone" cards depict robin's- egg-blue skies and impossibly pink sunsets above bridges, post offices, city halls, libraries and hospitals in Everytown, U.S.A. Nothing snide about these: a puppy's head wedged between halves of a roll with the words, "Hot Dog." A squeaking cat card with plastic eyes that blink when tilted. They're joyfully unsophisticated. But some of the oldies are beautifully drawn and tinted in pretty pastels: "Happy Birthday Dearest," wishes the sincere script above a lacy Victorian lady. Nazi memorabilia is hot. Black collectors seek out the blatantly bigoted cards about Negroes of half a century ago. Some feminists seek the staggering anti-suffragist cards. And Forties pin-up art cards are prized by connoisseurs of every political and apolitical stripe. At Antique Underground in P.G. Plaza, Marge Everson has sold out of $20 cards from a set of 48 with girlies representing each state of the Union, circa 1910. But she's still got a Lord's Prayer set of eight for $65 -- "in mint condition," although the pictures, mostly embossed angels and rosy- cheeked little girls, are "kind of maudlin." The impressive oldies postcard selection at Wish You Were Here in Baltimore's Harborplace includes many of an aging, now resurgent type: "Greetings from Biloxi!" -- six scenic shots in gaudy colors selling for five smackers. What makes collectors probe dusty bins at flea markets for shots of motel swimming pools, search junk sales for old Ron Reagan cards and sort through the "Christmas," "Humor," "Romance" or 50-state files at antique shops? It's the potential find. One woman discovered a card at an Alexandria yard sale postmarked Memphis, 1917. It's a Colortone of St. Vincent's Infirmary in Little Rock, Arkansas, where she was born. Dealer Everson suggests "people find the past through postcards." Her mail order business fills requests from all over the country for particular hometown cards. Some inquiries concern cards with postage cancelled on a ship or a train. Christmas Santa cards are very collectible," she says, "especially if he's in a suit any color but red." Capitol Beltway Postcard Club president Charles Collins has 3,200 more accessible postcard line seven years ago, partly motivated by an interest in printing errors. Recently Collins, a junior high school principal, and his wife, Donia, toured New England tracking postcards and buying them by the shoe-boxful. New-age kinky/trashy cards are also brisk sellers. In Alexandria, Cards Ink manager Robbie Ware stocks samples from all over the world ranging in tone from whacko to too-precious. "Our customers are mostly young professionals, not tourists, often in jogging suits. They'll be here for an hour at a time, and spend 78 cents or $20," she says. At Georgetown's Small Images, $3 pop-up cards include a colorful montage of Radio City, Times Square, Broadway and Grand Central fronts; there are 3-D cards, books of postcards of militant suffragettes, those omnipresent cat cards, famous photo cards, art cards, x-rated, gay and punk cards. Sal Mineo's pouty and James Dean's sullen beside a 1928 shot of Garbo by Edward Steichen that's purely elegant. On the other hand, a sloganeering item is a nuisance: "An idealist: one with idealistic but impractical ideas." The best trigger a response without words. One Georgetown University student perusing the R-rated samples at Small Images murmured, "Oh that's gross, these are weird." But another was hooked. "I never buy stationery, I just send cards," said G.U. sophomore Betsy Fisher. Like other fans, she often buys two of the same card, one to send, one to stash. Bernadine Styburski, who opened Small Images three years ago with Walter Draude to fulfill a small business fantasy, says most of their customers are "tired of pre-packaged sentiment. They're not sending cards out of form, they're thoughtful about what they buy." True card freaks would never think of waiting for someone's birthday to shop. Some bring visiting card fanciers on the receiving end of Small Images' inventory to meet Styburski and compare cards cataloged in their travels. One theory holds that sending a lively card guarantees a fresher return. Real fiends make pilgrimages to Untitled in New York, where Ken Harris has been accumulating an archive of art cards since 1966 and where customers sit on stools researching the racks, studiously scouting the works. "At any given time we have approximately 4,000 varieties to sell and another 6,000 samples in the back for museum researchers," he says. It took two years to track down a card reproduction of Georgia O'Keeffe's "Red Poppy" in St. Petersburg, Florida; he's sold several thousand copies since. None of Harris' cards is antique, and the most expensive postcard in the shop is 35 cents. Besides such nationally known manufacturers as Paper Moon Graphics, there are some local designers in the card game. Aqua Ink is three artists -- Ellen Zegar, Virginia Nichols and Ken Hobart -- who work out of a Capitol Hill home making a series of sleazy-tacky postal and greeting cards. "Mmmm, what a spread," is a typical tableau: plastic nude doll on salad greens, "bottoms up" swizzle stick in a glass, surrounded by knife and fork on a place setting of leopardskin. Another is a Fifties-style montage of a woman in a wolf suit leafing through True Confessions, a box of chocolates and a frothy drink on the Art Deco mirror table before her. Aqua Ink's new "Non-Traditional Christmas" line includes "Hark and the Herald Angels Sing," a black-faced rock act with the inscription, "Deck the Halls shoo-bop shoo-bop." Then there's a red- suited Santa spray-painting an alley wall: "Santa Lives." Zegar, a collector herself, says she snaps up "everything from Hollywood Wax Museum to hotel/motel cards. People will me their collections." Brian Cotton, a 20-year-old lo shot of Cotton's head being pushed into a chocolate cake. The step beyond card collecting is card conjuring. Inventive graphic designers cut up store-bought cards to make collages; Small Images' Styburski often sees samples of customers' cut-and-paste work. So clip, send or save 'em. But damn the November 1st postal rate hike and keep those cards coming. HAVING A GREAT TIME, WISH YOU WERE TOO DEPT.: "Islands I Have Known and Loved," a postcard show at Washington Women's Art Center, will accept cards from non-members to be exhibited October 27 through November 21. Cards must be postmarked between now and October 20; they become the property of WWAC, may be reproduced and cannot be returned. Drop them a line at 1821 Q Street NW. CAPITOL BELTWAY POSTCARD CLUB. Some 70 members meet from 6:30 to 10:30 on the second Thursday evening of each month at Greenbelt Junior High School to trade and sell cards. All manner of memorabilia change hands, from 10-cent "chromes" (with glossy fronts) to $200 to $500 "pioneers," dated before 1897. For further information call Charles Collins at 474-8942. WHERE TO FIND 'EM ANTIQUE UNDERGROUND, P.G. Plaza, Hyattsville. Wide selection of antique cards. 559-3000. BLUE MOON, 2435 18th Street NW. Vintage cards & contemporary graphics. 265-8113. BODY SCENTER, 1618 Wisconsin Avenue NW. Art Deco & funky. 965-3404. CARDS INK, 139 South Fairfax Street, Alexandria. A wide range of modern postal and greeting cards. 836-3688. COMMANDER SALAMANDER, 1420 Wisconsin Avenue NW. Specializing in funk. 333-9599. LITTLE CALEDONIA, 1419 Wisconsin Avenue NW. Modern, handmade and Victorian reproductions. 333-4700. PLEASURE CHEST LTD., 1063 Wisconsin Avenue, NW. X-rated. 333-8570. SMALL IMAGES, 3207 O Street NW. 333-0135. THORN TREE, 1305 Connecticut Avenue NW, 645 Pennsylvania Avenue SE and 3214 P Street NW. UNTITLED, 159 Prince Street, New York City. Art cards. 212/982-2088. WISH YOU WERE HERE, Harborplace, Baltimore. Antique and modern cards. 301/752-5169.