When 1,200 magicians gather in one place, they do what one magician does everyplace: fool whoever's in the immediate vicinity.

The place this week is a sternly guarded basement ballroom in the Washington Hilton where, as part of the 49th annual International Brotherhood of Magicians convention, some 60 dealers have set up booths pushing tricks that are guranteed to dazzle the eye and calm the soul. Or your money back.

It seems a bit odd to be entering this sanctorum, this front of magical knowledge from which laymen are strictly forbidden to drink. Yet worry is needless. Tricks are demonstrated but not explained. For that you have to pay ready money.

This year, dealers have come from as far away as Belgium, England and even India - Bombay's D.A. Tayade features specially lacquered Indian rice vases and something called a Foo Can - to compete with reknowned American magicians like Albert Goshman, as in "Magic By Gosh," a man who says "I don't know if it's true, but my mother tells me I came out of the womb holding coins in my hands."

Prospective buyers are especially demanding here, complaining that magic wands now make do with plastic tips, wondering if tricks are "examinable," ie. able to withstand the withering eye of a cynical public, and in general saying things like "The presentation was great, but it's a terrible trick. If I did that to an audience they'd lynch me."

And though a large ad for "Phil Moore's NEW 'Slicing A Lady In Half' - May be transported in the back seat of an automobile" - is in the convention program, the fact is that type of mystification is now the exception, not the rule.

Almost gone are the days of Big Magic, when Calvin Coolidge had his smashed watch reappear whole inside a loaf of bread, when Harry Houdini forced his assistants to sign notarized oaths of secrecy. "In our world a lot of things surprise us - what can be more surprising than men walking on the moon?" Says Dr. Peter Wersten, a magician whose appearance from East Berlin is pretty surprising itself. "Now you have to entertain with magic. That is what is most important."

"No one can afford to carry a trainload of effects with him. Most magicians go on with a small box," says Trevor Lewis, a specialist in children's magic from Gwynedd, Wales, who has done tricks extolling road safety and one about a boy who would rather eat lollipops than brush his teeth and ends up being called "Waneta" because he has only "one eater" left in his mouth. "You depend more on your own personality: If you can't project, you can't work."

And what does Lewis think about the state of the art today? "Well," he says slyly, "I'm teaching my boy magic in case it ever makes a comeback."