Let me call you sweetheart. The romantic and gentlemanly world of barbershop singing

People who like barbershop singing really like it. Every year, on the July 4 weekend, the Society for the Preservation and Encouragement of Barbershop Quartet Singing in America holds a convention somewhere, and people come fully prepared to live, eat, sleep, and breathe to the sound of a ringing barbershop chord. It's been happening for 49 years now.

This year, Hartford's Civic Center was packed with 10 000 friendly barbershoppers and their spouses, the former wearing light windbreakers and doubleknit shirts (mustaches are popular) and bearing name tags that show what part they sing: tenor, lead, baritone or bass.

The visitor is seldom out of earshot of singing, as everywhere you walk there are little knots of four men - with perhaps a superfluous baritone or lead cozying up hopefully - giving heart and soul to ``Sweet and Lovely'' or ``My Wild Irish Rose.''

Songs like this are called ``barberpole cat'' songs, which just means that they are songs that every barbershopper knows his own part to. Complete strangers will sing together for a while, chat a minute, shake hands and drift apart again; ``Nice singing with you,'' they say, by way of farewell. Barbershop songs tend to be gentlemanly and sentimental; references to ``skies of blue'' and ``dear old dad'' float clear and sweet above the din.

Don Hewey from Worcester, Mass., said that the impromptu songfest goes on all weekend. ``At 4 in the morning, there'll be singing going on everywhere. We are a little bit fanatical about it, but that's why it's so much fun,'' he said. ``Saturday night's the blowout - you sing until you can't sing anymore. Then you sit around and wait for next year.''

Mr. Hewey was on hand for the Massed Sing, a traditional kickoff for the weekend. There is a stunning simplicity to the sound of thousands of male voices filling the air of the convention center rotunda with ``Shine on Harvest Moon'' and ``Let Me Call You Sweetheart'' in four-part harmony; it is the aural equivalent of the Grand Canyon.

During the national anthems of the United States, Canada, and Britain (with newcomer Sweden, the countries participating in the convention), women are invited to join; there is something dreamlike about having people peel off into chords all around you, like performing in a concert when you haven't been to any of the rehearsals.

The official entertainment consists of a series of contests to pick the year's superlative quartet and ne plus ultra chorus. At stake, within the world of barbershop, are fame and fortune: the high-placed groups are booked at barbershop events for years in advance all over the US.

The contests last all afternoon and into the night.

The first thing you notice is that different quartets have different personalities. Some are suave: like the Chicago Chord of Trade, in black tuxedoes and pink lam'e bow ties, and the beaming and genial air of what used to be called ``men about town,'' singing ``There's Something I Like about Broadway.'' Some are vibrant: the Interstate Rivals singing ``The Little Boy (I Used to Be)'' in tones so brilliant the ceiling rings like a gigantic bell. Others are humorous: the 139th Street Quartet singing ``If I Were You I'd Fall in Love With Me,'' wearing red letter sweaters, beanies, and, amazingly, fake buck teeth. ``That takes some doing, that does,'' said Don Terry, who was sitting next to me.

Each lift of the hand or tilt of the head has obviously been practiced for hours. There are judges for each of four categories: sound, of course, stage presence, interpretation, and song arrangement. (Songs can be new, but they must be in the barbershop style: old-fashioned sentiment, simple lyrics, and lots of flatted seventh chords).

James Richards, one of three sound-judges, said that in his case, the question ``What do you look for'' missed the crucial point. ``We keep our heads down most of the time,'' he said. ``We listen for something we call `expanded sound.' It's not in any music dictionary. You hear a block of sound coming toward you - you can't really tell whose singing what part: It blends.''

Part of the distinctiveness of the barbershop sound comes from the fact that tenor sings above the melody. Also, there is a certain sound that really brings the house down; it is brilliant and ringing, with all four parts trumpetlike and distinct. Al Carter, a tenor from Georgia, said that one thing barbershop devotees listen for is something called ``overtones.'' ``[When all] four parts are close together, they'll actually generate tones that no one is singing,'' he said.

Even more amazing and wonderful than the quartets are the choruses. Said Mr. Terry, ``I have been to chorus contests that were so good, it sounded like a giant quartet.'' In most choruses you are merely a black and white shape with a voice, but here there is a kind of choreographed individuality: Everybody emotes on cue.

During the semifinals the OK Chorale from Oklahoma, in red shirts, gray velvet jackets, and cowboy neckerchiefs, sang a bouncy slapstick song about being hanged called ``If They String Me Up I'll Never Live It Down,'' and then a quiet and sustained version of ``Forgive Me.'' At the end of ``Forgive Me'' they suddenly froze into big shaggy howdy smiles. It takes a lot of practice to get 100 people to smile in unison. ``They may not win, but that's about as good as it gets,'' said Mr. Terry.

The Big Apple Chorus from New York, dressed in silver and white, sang ``I Wouldn't Trade the Silver in My Mother's Hair (For All the Gold in the World'') with a smooth perfection that was professional, except you felt that they were really giving it their all, not just trying to look as if they were.

``The degree of perfection sought by the best of our choruses is really remarkable,'' said judge Glenn Van Tassell, an elegant man who has been in two gold-medal-winning quartets. ``It all comes out of a great love of music. This great perfection is coming out of people who are in fact plumbers, electricians - reporters; people from all walks of life. ... Those of us who see a lot of kinds of music believe that there isn't anything quite like this.''

That evening, during the finals, everybody - chorus and quartet - was so good it seemed they all deserved to win. The Interstate Rivals, in white suits and blue bow ties, sang ``Forgive Me'' and ``I'm Sorry I Said Goodbye'' in bright ringing tones that got an ovation (``That's a winner,'' said a man next to me.) The Chiefs of Staff, in red blazers and blue lam'e vests, sang ``I'm Lonesome, (That's All),'' in more ringing tones that inspired screams of applause.

Then the choruses: the Thoroughbreds, in black tie with a red rose in the lapel, sang ``Your Nobody's Sweetheart Now,'' sounding just like a giant quartet. The Big Apple Chorus, in red with gold lapels, sang a precision-edged version of ``My Cutie's Due at 2:22 Today.''

The West Towns Chorus, in white, with red metallic bow ties, sang a George M. Cohan medley; in perfect time, they flipped the jackets open to reveal red-white-and-blue sequined vests, to gasps from the crowd.

Now, that's entertainment, you think.

The judges' entries are quickly compiled by computer, and the winners are announced. First-place chorus: West Towns Chorus; first-place quartet: the Interstate Rivals.