A stethoscope snakes its way through Barry Hansen's beard.

It is a smybol of laugh therapy -- and of the way that Hansen, better known over the airwaves as Dr. Demento, catches the comic pulse of pop music.

His weekly two-hour "Dr. Demento Radio Show" is marked by manic patter sandwiched between layers of Spike Jones, Monty Python and hundreds of deservedly unknown but irrepressible zanies who have been committed to vinyl. The show is rated No. 1 in the huge Los Angeles market, and is currently heard in 125 other markets, including the local WAVA-FM (105.1).

Tomorrow's 10 p.m. broadcast will mark the Doctor's 10th anniversary on the air. He first started playing his "odd" songs on California's KPPC in 1970, in the heyday of free-from radio. At that time, no one had yet explored the funny underside of the musice business. "After the first commercial of my first show, right after I'd played Nervous Norvus' 1956 hit, 'Transfusion,' the station's secretary said 'You've got to be demented for playing that on the radio,'" recalls Hansen.

"Everyone else at the station had a name -- Outrageous Nevada, The Obscene Stephen Clean -- so I became Dr. Demento. Now that radio has become so tightly formatted, I've sort of inherited the whole field." After two years of rising success, he was approached with an offer to syndicate the show in 1972, and the rest is history, including his national tours.

He opened a 17-city college and club tour with some wild platter-spinning Wednesday night at Desperado's. One of the reasons Hansen/Demento takes to the road is to "play the songs I can't play on my show."

Though Hansen, 39, collects "everything" (his record collection has passed the 150,000 mark), his fame has come in the area of novelty music. His non-toll-free request line averages 1,000 calls a week, some from as far away as Australia and New Zealand (where the syndicated show is carried).

Among the most requested songs: "Pencilnecked Geek" by Fred Blassie, "Fishheads" by Barnes and Barnes, "The Nixorcist," and more recently, "Another One Rides the Bus" and "My-my-my-my-my Balogna" parodies of Queen and the Knack, respectively if not respectfully, and a new, timely "Space Invaders."

Occasionally, Hansen has had to take a popular selection off the air -- as he did last when he played a song by Little Roger and the Goosebumps called "Stairway to Gilligan's Island." Led Zeppelin took exception to the hilarious parody of their "Stairway to Heaven" (the most popular rock song in radio history) and threatened a lawsuit.

Much of Hansen's material comes from listeners inspired by the program. Several of the hundreds of records and tapes -- most notably Larry Groce's "Junkfood Junkie" -- have moved from homemade tape to hit single by way of Demento. The material, says Hansen, runs the gamut from "genius to misdirected inspiration. I have seen basic no-nos, beyond the fact that some of these songs are unplayable on commercial radio today." They include obscenity, overt endorsement of hard drugs or racism, libel or slander of persons or commercial products.

If he needs more material, Hansen need look no farther than his monstrous collection of records. "There's a house where the records live," he says, "and incidentally there's a place where I sleep." Growing up in Minneapolis, he became interested in records when he was 4 and his parents built a footstool in front of their radio/phonograph console. "I could have tinkled around on the piano, but when I put a record on, I could make the whole orchestra play."

His obsession began is earnest "when my parents put me into a school that required a trolley ride across town and it passed a store that had a sign saying 'Used Records -- 19 cents.' I existed for many years on two meals a day because my lunch money went to records. A year later I took a difference trolley home and passed a Salvation Army store which had a sign saying 'Records, half-price, two for a nickel.'" He was hooked.

After picking up a master's degree from UCLA (in folk music), Hansen worked over the years in many corners of the music field. As a writer, he has appeared in Hit Parader and Rolling Stone. He was the original lone writer of what eventually became the multi-author "Rolling Stone Illustrated History of Rock and Roll."

"I got as far as 1967," he sighs, "by which time it was 1972."

He produced a 35-record reissue series of vintage gospel, blues and rock 'n' roll for the Specialty label, an album by guitarist John Fahey, and more than a dozen of the celebrated Warner Bros. "loss leader" sampler albums. He has served as a consultant to performing historians like Ry Cooder and the Blues Brothers, and for films as well. "Randy Newman needed certain types of songs for his 'Ragtime' score, so I ran off a tape as a guide to the music of the period."

He has two albums of his own and a deal under way for a book on rock 'n' roll history. It's likely that the radio show will expand to TV. But for now, there's radio.

"The imagination of my listeners knows no bounds," says Hansen. "I see my show as dessert after a week-long meal of meat-and-potatoes rock 'n' roll."