"let me retune it," says Jim Turner as he stands against the wall of the National Museum of American History's hospitality suite with a table full of brandy snifters.

The museum's Holiday Celebration -- which will continue through Wednesday -- is going full force outside the tall doors with the Rochelle Helzner Quartet. Strains of its Jewish folk music drift in each time one of the 2 dozen Takoma Mandoleers enters, so Turner must concentrate on his tuning. He dips a giant syringe into a platic jug and squirts some water into one of 40 snifters arranged meticulously on a wooden table, then rubs his fingers around the rim until the friction creates a gentle hum or clear harmonic.

No, he's not the caterer setting up; no, he's not a dealer in antique glassware. Jim Turner is one of the best -- and one of the few -- players of the glass harp.

Turner is one of several hundred musicians and craftspeople who have transformed the American History building into a living museum. The 40-year-old performer, who looks a little like a clean-shaven and healthy Abe Lincoln and speaks with the enthusiasm of a believer, is no stranger to Washington. Eighteen months ago, he performed at the Renwick Gallery on the singing saw and the wrench harp (made possible in large part through the generosity of the John Deere Co., which donated almost $1,000 worth of wrenches). This year, Turner has come to town with another unique, dare one say esoteric, instrument that he only began to learn 3 1/2 years ago.

"But it's a very old tradition that goes back at least 300 years the way I play it," he proudly points out. Glass instruments had their heyday in the late 1700s, when Benjamin Franklin invented the glass harmonica, a series of graduated, tune glass bowls based on the centuries-old "goblet" system that Turner plays. Mozart wrote several of his last compositions for the instrument, including a beautiful adagio for Franklin, which Turner played yesterday; Beethoven composed it, as did Christoph Gluck. But Franklin's adaptation, which for a short period was as popular as the piano-forte, fell into disuse when a number of its virtuoso performers developed strange nervous disorders ("overtone vibrations, maybe lead poisoning from the glazes and paint of the time," Turner theorizes).

Judging from the smiles of Turner and his audience, there are apparently no ill effects from either playing or listening to the glass harp. In his hour-long performance yesterday at the Museum (repeated today and tomorrow at 1 p.m.), he evoked sounds of a calliope, a barely bowed violin or even a softly played sackbut.He touched down on the Renaissance, a "Greensleeves" with enough variations to make Vaughan Williams happy, "You Light Up My Life," several Japanese folk songs, a polka, "Hava Nagela," a pair of baroque melodies, "When the Saints Go Marching In," a cakewalk, a few Christmas carols . . . a mood for each glass, almost.

"The instrument is exciting for me because it expresses a basic philosophy that I have: There's a tremendous uncommonness in each common thing -- and of course, that's specifically important about human beings," says the man who's working, with his wife Mary, toward a doctorate in creative arts education at Rutgers. "This," he adds, sweeping his hands gently over his array of glasses, "expresses that in a very basic way -- an ordinary glass, not expensive crystal. And yet, out of that comes an extraordinary sound. Each person has that same potential, it's just a matter of allowing them to express it."

Turner's quest for the perfect receptacle has not been easy. Of his 40 glasses, only six are crystal ("with almost no lead . . . good crystal tends to ring too long, and you don't have control over your instrument") and into them he pours only distilled water ("It's like good rosin on a violin bow"). Turner must even watch where he washes his hands: "If the water's too soft, it'll mess up, it becomes too slick. My fingers have to be really squeaky clean, that's quite important." Hand lotions are out.

And then there are the salespeople. "I do audition them [the glasses]," he admits. "I carry a pitchpipe, a little bottle of distilled water and a rag or dishcloth. Then I ask them if I can try the glasses. Once I found a D and a D sharp in the high register that had just come in from Romania, but the salesgirl at that particular store must have thought my bottle held something besides water. She looked affronted: 'Sir, you can't do that sort of thing in here.'"

Turner only uses brandy snifters -- they carry twice the volume of wine glasses. His harp has a range of 2 1/2 octaves and is arranged for both single-note playing and chord clusters. When he plays -- actually, even when he tunes -- Turner has smiles on the tips of his fingers. "I've been a musician all my life," he explains, tracing his musical journey back to high school in Lewistown, Mont., and "ordinary" instruments like the clarinet and piano. But when his high school performed Marylou Knapp's "Down to Earth," Turner volunteered to fulfill the stage direction for a musical saw. "I swiped my Mom's violin bow and the janitor's saw, and in 2 1/2 weeks I got a sound."

Accepting the challenge of the band director ("He said, "I'll let you play in the band when you can play a chromatic scale') Turner practiced secretly until he could walk in one day with a saw instead of a clarinet. Talent shows followed, and he got increasingly serious about the saw, to the point where he has performed with the Denver Symphony Orchestra and the Boulder Philharmonic, whose director David Burge has written a concerto for Turner ("there's something about getting up in front of an orchestra with a hand saw, it's a marvelous experience").

Turner's aim now is to "expand the instrument's [the glass harp's] great potential." Although the classical repertoire is limited and occasionally hard to dig out of the archives, the potential for adapting other music to the instrument is infinite: "It's like a giant fishmarket," he insists. And 1981 looks like a promising time to go fishing. In the past two years, Turner's played with a number of Rocky Mountain regional orchestras; this year will find him at many colleges, playing pop, blues and classical melodies not only on the glass harp and saw, but on the contrabass clarinet ("five feet tall with a wonderful, resonant bass sound," he enthuses). He'll also be one of the first guests on a new CBS series, debuting in January, called "That's My Line." "I didn't want to be on 'Real People' or 'That's Incredible.' They really put down a lot of the performers they feature. It's such a special sound, I don't want it used as a gimmick."

And when the show is over, it's not bottoms up and into the dishwasher. "I wash them all by hand," says Turner. And there's no doubt that he dries them with love.