IF YOU WANT immediate proof that Washington's been home to a strong homemade-music community for a long time -- and that Washington is simultaneously undergoing a renewed interest in acoustic/folk music -- you don't have to believe what you read in the papers. Turn on the radio.

This weekend. Even during the week. Just not Q-107.

Start at 6 p.m. Saturday. Tune to WETA-FM (90.9) and you will run into the ever-more-popular public-radio variety program, Prairie Home Companion. Here, you will also find that well-known host Garrison Keillor's homespun wit is leavened by liberal portions of less-well-known acoustic folk and blues performers. What a complementary arrangement. And what a complementary lead-in to:

"Traditions," Mary Cliff's five-hour WETA digest of traditional folk, ethnic and acoustic music, notes and meanderings -- one of the two best-known and longest-running such specialty programs on the air in Washington (the other being Dick Cerri's "Music Americana"). It starts at 8 p.m. Saturday.

Cliff's "Traditions," 13 years old this year, takes its name seriously -- but also reflects the homey, hip and front-porch- friendly persona of its sole proprietor. So while Cerri will describe the upcoming Peter, Paul & Mary concert as a "heckuva show," Cliff is the one who'll mention that, oh by the way, it's also a Free South Africa benefit, and the reason Louis Gossett Jr. will be there is that he's known the trio since its beginnings in Greenwich Village, and so forth. And then she'll air a thoroughly telling, 11/2-hour PP&M mini-documentary, which she put together herself from recent interviews, plus her extensive personal collections -- of acoustic recordings, and of a harder-to-find commodity known as perspective.

Since she's the entire on-air, off-air staff of the program (plus she answers phones and clps the newspaper concert ads herself), Cliff puts everything together herself for "Traditions," including the who's-where calendar -- among the best and most treasure-filled anywhere, spanning everything from square dances to big-name folk acts at the Birchmere and Wolf Trap, to a Brazilian samba party, to Southside Johnny at the Bayou.

"There are two things that the show does, that have evolved naturally over the years," Cliff says. "One has been keeping the community in touch with itself -- kind of a folk-music community bulletin board thing . . .

"The other has mostly been putting the music in its proper context -- putting, among others, our singer-songwriter types, our homemade music types, together with the musical movements they come from, or are related to -- all, hopefully, without getting stuffy."

Cliff herself is never stuffy, sounding sprightly and comfy on just about any branch of folk's ever-sprawling family tree, ut she does often veer -- into, say, 20-minute sets of nothing but West Virginia fiddle ditties, or a show-ending hour of Vietnamese Tet (New Year's) music. But these unpredictable, generally premeditated swings -- from something topical by Si Kahn or Tom Paxton, to something Appalachian by Cathy Fink, to something unexpectedly quaint, but hip, by a South African acappella gospel group called Ladysmith Black Mambazo -- are what can make an occasional Saturday night with Mary Cliff a real homebound treat. Not just good -- but good for you.

Dick Cerri's "Music Americana" (8 to 11:30 p.m. Sundays on WLTT-FM/94.7), on the other hand, is mostly good -- meaning popular, meaning listenable, and meaning you'll hear lots of nostalgic Kingston Trio, Limeliters, Peter, Paul & Mary tunes, and lots of newer folk -- with a definite pop twist. And lots of commercials for such Americana as Chevys, Ourisman Fords, Riggs Banks and Best Products.

No one's complaining, commercials being evidence of good ratings, and Cerri being sincerely interested in opening listeners' ears to the kind of music that doesn't leave those ears a-ringing. And he's been especially successful lately -- through the smart combination of his radio outlet, his monthly "Music Americana" showcases of local talent (with out-of-town headliners, usually) at the Birchmere these past two years, and the formation of a nonprofit promotional organization, modestly named the World Folk Music Association.

Cerri's folk-pop radio show turned 25 this year -- though it wasn't always 31/2 hours long nor quite so successful as it is nowadays. (The anniversary was celebrated in an engaging, impressive concert at Lisner last month; performers included such veterans as Tom Rush, Paxton, Jonathan Edwards, the Seldom Scene, Cathy Fink, Bob Gibson, Steve Gillette and a surprise reunion of the Chad Mitchell Trio, plus such up-and- coming acts, local and otherwise, as Christine Lavin, Schooner Fare, Mary Chapin Carpenter and John Jennings, Pete Kennedy, razz Matazz, Mountain Laurel and Buskin & Batteau.)

Aside from his nostalgic, pop-folk base, Cerri also plays a good deal of new acoustic music -- there being more new acoustic music around to play, and much of it being melodic, intense and well crafted (and yes, catchy). These are the artists Cerri's helped popularize in Washington, among others: Maine's Schooner Fare, Boston's Bill Morrissey, San Francisco's Kate Wolf, and New York's Christine Lavin and Buskin & Batteau.

"What Dick's been doing is great," says Lavin, who alternates -- on and off stage -- between boisterous enthusiasm and wicked wit. "The audiences in Washington have been fantastically responsive."

Buskin & Batteau, no slouches in the wit department, until this year had not played D.C. except as sidemen for Tom Rush. They played one of Cerri's recent showcases, and they headline at the Birchmere March 29.

Sit through one performance of, say, violinist Robin Batteau's "The Boy With The Violin" -- their best-known original -- and you'll reconsider any notions that folk is automatically diluted, rather than strengthened, by pop sensibilities.

"Folk audiences are smart," says Batteau. "They're different from rock audiences -- which don't listen to anything but rock. Or classical audiences -- which listen only to classical. Folk audiences listen to everything."

ALSO ON THE AIR

* WAMU-FM (88.5) is a big acoustic outlet, but its weekday presence is heavily into bluegrass and honky-tonk -- particularly late in the afternoons. From 1 to 3 p.m. weekdays, though, about a fifth of what early-afternoon host Lee Michael Dempsey plays is acoustic folk, new and old, not quite bluegrass and thoroughly enjoyable (and intelligently framed by Dempsey). Also, try "Bluegrass Overnight" (Saturday nights, midnight to 6 a.m.) especially every third weekend, when it's hosted by Carol Pittard (this is one of those weekends). Folk and blues roots are traced Sundays on WAMU, from 11 a.m. to 2 p.m., by Dick Spottswood, and Celtic folk is the specialty of the hour-long "Thistle and Shamrock," Saturdays at 11 p.m.

* WMAL-AM (630) is starting its own folk-acoustic music show this Saturday; you know the genre's got to be Hot. It couldn't have happened to a more attentive WMAL personality, however -- that being John Lyon, an acoustic musician himself from way back, whose "American Showcase" (hmmm) airs 12:30 to 2 p.m. "God bless Dick Cerri and Mary Cliff," says Lyon, whose program will incorporate music, interviews and his own rumblings on American music. "I remember when you used to be able to go to the House of Musical Traditions and be the only guy in there for an hour and a half. Now you can't even get into the place. People'll be comin' in saying, 'I heard this on so-and-so's show, do you have it here?'"

They usually do.