When I first heard that Portland’s downtown merchants were using classical music as a weapon in their war on juvenile loitering, I immediately thought: opera.

In my experience, nothing disperses kids quicker than a soprano screeching her way through a Puccini aria. Sends the little tykes fleeing like rats from a burning barge.

But I’m getting ahead of myself. Let me back up a bit and explain.

According to a recent Associated Press story, the Portland merchants were tired of having groups of teen-agers hanging around near their stores, clogging up the pedestrian walkways and making a nuisance of themselves. Bad for business and all that. In checking with other cities around the country, a group called the Downtown Improvement District learned that classical music piped outdoors has been proved to have an interesting psychological effect on many young people — it makes them want to scatter.

So the Portland business group set up a couple of speakers over Monument Square, tuned in a local classical station, and proceeded to blast the youngsters with Schubert’s “Grand Duo in C.” Most of the loiterers found the stuff so revolting that they eventually grabbed their skateboards and skulked away, grumbling.

The idea was not entirely new, however. The story quoted a 7-Eleven company spokeswoman who said the chain has used music as a loitering deterrent for three years now. Muzak, Montovani and even country-and-western seem to be highly effective. It’s simple, she said: Just figure out who your audience is and then play the music they despise.

Yet the program director of WPKM, the station that provided the music in Monument Square, told me he thought the plan might backfire on the store owners.

“The kids might actually get to like classical music,” John Spritz said. “Next thing you know they’d be having classical concerts and teaching the waltz and the minuet in the square.”

Not a bad idea, but pretty unlikely. To many youngsters raised on heavy metal, punk and rap, classical music is comparable to the maddening water-dripping-on-the-forehead torture used on prisoners in World War II. It is mind-numbing monotony that can drive them nuts. Knowing the effect that opera has on my own children, for instance, I think the Portland idea could work.

If it catches on, other cities with loitering problems — cities such as Bangor — would probably want to try it. If so, a cassette tape might be handy. On it would be a selection of classical pieces guaranteed to make young people cover their ears and shuffle off to more hospitable surroundings. The tape could be called “Crowd Control Through the Classics,” or “Classical Dispersion: Music to Clear a Plaza By.”

When I asked John Spritz what music would fit the bill, he quickly suggested the Bruckner symphonies.

“Playing all the symphonies back to back, which would take about 15 hours, would really make young people think twice about lingering in one area for long.”

Victor Hathaway, who does a classical-music program on MPBN radio, said opera probably had the greatest potential to move people — to move them right out of your downtown, that is.

“After opera, probably anything with solo harpsichord. That’s irritating,” he said. “Or maybe organ music. J.S. Bach’s Goldberg variations could work, too. They were actually written as a soporific, something to put a nobleman named Goldberg to sleep. And Mahler might be worth a try, although I would agree that Bruckner is infinitely more boring than Mahler.”

Hathaway said that to make an effective anti-loitering tape, something truly odious and repulsive to teen-age ears, it is necessary to avoid playing certain classical pieces that might create the opposite effect. He recommends refraining from Wagner’s “The Flight of the Valkyries,” which, as the movie “Apocalyse Now” made clear, has the potential to stir fierce warring passions. And Ravel’s “Bolero” is definitely out, too, considering what the piece did to Dudley Moore and Bo Derek in the movie “10.” Loitering is bad enough without that.

“Actually, I don’t think I’d use classical music at all,” Hathaway said. “It’s too good, and the loiterers might begin to understand it and like it. I think you really have to go with elevator music — `The 101 Strings’ or Muzak stuff like `Raindrops Keep Falling on My Head.’ ”

I think that might be a little too strong. After all, the idea is not to make everyone run away from the downtown.