"EV RY BO DY . . ." sand John Ondish, who builds exhibits at the Smithsonian.

"Boom, boom, boom," harmonized tenor (and schoolteacher) Rick Moock, baritone (and chemical engineer) Norman Hollies, and bass (salesman) Art Rounds.

". . . Loves a lover," continued Ondish, with the other voices weaving around his melodic line in a unique style that is as quintessentially American as the sound of a banjo. The Close Enough were warming up for the 32nd annual Harvest of Harmony of the D.C. chapter of the SPEBSQSA.

That's the Society for the Preservation and Encouragement of Barber Shop Quartet Singing in America, and seven of its groups and a chorus, will raise their voices at 8 tonight in Constitution Hall.

"There's a lot of conversation in our society," said Lews Sims, baritone with the Federal City Four. "Are we a musical society plus fun or a fun society plus music? It comes out about 50-50.

The Federal City Four, also warming up for tonight, stands at an opposite pole from the Close Enough in the concordant but individualistic world of quartet singing. The Close Enough, a relatively young group which has been singing together for five years, emphasizes the fun half of it, with comedy routines, straw hats, striped shirts and some numbers featuring beautifully crafted puppets that will strike a responsive chord in Muppets fan. "We try to make it funny because we don't sing very well," said one of the foursome, obviously not meaning a word of it.

The Federal City Four, together since "one morning at 2 a.m. in 1961," is an older group, all retired now, so that they can do a lot of daytime work singing in schools, hospitals, homes for the aged. The years together have refined their ensemble to the smoothness of a single voice, and they emphasize the musical 50 percent of the barbership phenomenon.

But in spite of such differences, there is a harmony between the young group and the old-timers - a harmony so close that a singer from one group can seamlessly fill a gap in the other on a few minute's notice.

The origins of the form are lost in antiquity. It has affinities with traditional styles of unaccompanied religious singing, particularly in the South, or with the a capella antemse that William Billings was writing in New England during the Revolution.

But the barbershop style is harmonically distinct. It is homogeneous, using male or female voices exclusively. "Women's groups have their own national organization, the Sweet Adelines, which is friendly but not affiliated with the SPEBSQSA.) It always has a "tenor" part singing harmony above the melody as well as two low voice under it - and arangement more often heard in late medieval music than in modern style.

According to the theory most popular among singers, the name arose in the all-male ambience of the barbershop, where men used to go each morning to be properly shaved. The customers waiting for their turn would while away the time by singing old songs, and the style evolved from the situation and personnel available. Others think it may have developed in firehouses. In either case, the two essential elements were an all-male environment and idle time to be filled. But there are other important social factors as well.

"An active quartet really has to be an octet," according to Fred Peters, lead singer of the Federal City Four. "Besides the four singers, there are four wives, and it's hard to keep a quartet together if their wives don't get along."

Quartets rehearse once a week in the members' homes, besides a weekly meeting of the local chapter (the D.C. group meets on Monday nights in St. Paul's Lutheran Church on Connecticut Ave.), and some quartets find themselves taking joint vacations and otherwise merging their social lives.

"Quartet singers have to have the most understanding wives in the world," said one of the singers, and the others nodded in four-part harmony.

In 1936, when Norman Rockwell painted a nostalgic Saturday Evening Post cover showing a quartet singing in a barbershop - one man's face still half-covered with lather - it seemed to be a dying art. Radio had reached its prime, and people were beginning to think that music was something that came out of a little box with wires, not something that people made at home for their own enjoyment.

So two years later, in Tulsa, Okla., a tax attorney named Owen Clifton Cash founded the society, as its name indicates, to preserve and encourage this folk art. Cash's efforts caught on, reversed the trend, and today the society - headquartered in Kenosha, Wisc., - has 750 chapters with 38,000 members in the United States and has spread to Canada, England and Australia. (Barbershop quartets have never caught on outside the English-speaking world.) The national organization has given more than $2 million to a Wichita speech therapy clinic, confirming its motto: "We sing . . . that they shall speak."

Cash gave himself a mock-dignified title to match the society's initials: Temporary Permanent Third Assistant Secretary. His name and that title are on the charter of the D.C. chapter, which was founded in 1945 and now has half-dozen offspring - "just about one for every county around here," according to a member. The D.C. chapter has "a higher concentration of PhDs than any other in the country," he said. "But we've never had a barber."

Recruitment of new members is no problem, "once they hear the sound," said Rick Moock, and Art Rounds added that barbershop harmony "can become an addiction - you get so that you need a fix now and then. Our society is full of people who are looking for the lost chord."

The distinctive chords of barbershop harmony, in fact, have been lost in most other music. There is a special sweetness in this harmony because it is - or should be - always sung perfectly in tune. This is not as common as the casual listener might expect. For centuries, the basic sound of Western music has been tempered to make allowances for the sound of keyboard instruments. Because a piano, for example, does not distinguish between C sharp and D flat, as the human voice can every well-tempered clavier has to be tuned microscopically out of tune.

"They didn't have pianos in those old barbershops where customers would sing harmony while they were waiting for their morning shave," explained one quartet member, "so the voices were able to sing a true diatonic scale, not a tempered scale." Listening to the music, even with out knowing the reason, the ear hears the pure harmonies and is grateful.