If you had to square-dance in your high school gym class on rainy days, or went to the Saturday night dances in the firehouse and sat on the windowsill between sets to get cool, you might not be ready for this.

"Wheel and deal," shouts the caller, "touch your quarter, pass through, step to an ocean wave . . . Boys, explode your wave, girls, partners trade . . . Everybody do a diamond circulate . . . Grand right and left -- and swirl."

There are 68 basic movements in the Mainstream level, and some 4,000 variations. It might take you two years to progress to the Plus level, and beyond that are Advanced and Challenge. There is a Callers Lab, attended by perhaps a quarter of the nation's 5,000 professional callers, and it is here that the steps and their names are worked out and standardized. This is western-style dancing, which emerged in the mid-'50s and spread not only to Canada but also to Europe, Australia and even Japan, American calls and all.

Square dancing has come a long way from the courtly reels of Revolutionary days and the wagon train scene of the classic westerns with tough old trail hands galumphing around to the scraping of a fiddle.

Square dancing has come a long way from your high school gym class, too.

"To think modern square dancing is just 'do-si-do' and 'allemande left' is like thinking the Redskins just say 'Everybody go out for a pass,' " says caller Dick Bayer of Fenton, Mich.

Nearly 3,000 people in western shirts, string ties and short skirts as frilly as iceberg lettuce have filled to bursting the Sheraton Washington this weekend for the 26th spring festival of the Washington Area Square Dancers Cooperative Association.

That's nothing. Almost 10 times as many attend the national festivals, held every year in a different city around the country.

They are a cheerful group from all over the East, including the Touring Squares, who chartered a bus from Hartford, Conn. They don't hold meetings or lectures or competitions. All they do is dance.

And talk. They do talk a lot. Get them out on the floors of the six ballrooms they have reserved, get them set up in their four-couple squares, and every minute they aren't dancing, they talk.

"These are friendly people," said Bayer, one of the eight callers here. "You go on vacation and you look up a club to dance with in another city, and they're apt to invite you over for dinner and to stay the night."

Lasting friendships grow out of these meetings, which are simply an extension of the local clubs. A dancing couple might belong to the Haylofters, the Redland Rounders, the Barnstormers, the Dale City Stompers or another of the 170 Washington area clubs, or several at once, but every year they meet new people at the festival. For the relatively few singles who attend, there is a Hitching Post for temporary partners.

They are of all ages, mostly in their thirties and forties, and they hate to hear the media patronize them as old folks. Though, along with the teen clubs and family clubs and camping-dancing clubs, there are indeed clubs whose members are 80 and up.

"The great thing about this," said Garnett Reilly of Fairfax, whose husband Jerry is assistant director of the festival, "is that you can take your dance clothes in the car on vacation, and when you find a group to dance with, you know you'll understand the calls and movements."

Some prefer round dancing, which is close to ballroom dancing except that all the couples form a large circle, moving in unison to "cues" by a "leader." The music is swing rather than the country-western that dominates square dancing, and the terms are somewhat less colorful: reverse impetus, banjo position, heel turn, progressive chausse'e, chausse'e roll, fishtail, change display and so on. It is equally standardized, and the three leaders at the festival, like most of the callers, are professionals.

In the enormous Sheraton ballroom, at least 1,000 Plus-level dancers (the biggest group by far) are having a workshop under Dave Taylor, an Illinois caller who has worked all over the world in his 31 years in the business. He quiets the talkers with a little recorded music -- that's another thing: there are no bands, just hundreds of records, with 15 to 20 new releases a month -- and starts to teach them a step called "acey deucey."

This is the first movement they have to learn to progress to the Advanced level. But many people here aren't that determined to move up. They just like to dance. And when they learn a new step and find themselves, after all those complex twistings and interweavings, right back where they started, it's a great feeling.

As the whole roomful of colorfully dressed people starts to spin and turn and make wheels within wheels, it is apparent that some things never change. The caller's patter is as jaunty as ever it was in a New Hampshire hoedown, the dancers are "boys and girls," and when the men are momentarily paired off Taylor remarks, "You'll notice your partners aren't as good-lookin' as they were."

As in the old days, the young men step higher, spin partners harder, slap hands louder. The veterans move with tidy precision, backs straight, faces intent. A few old hands add rococo gestures as they sweep their ladies into a promenade. A few of the skirts rise high enough to reveal red panties.

In every ballroom stands a large coffee urn filled with water. Dancers drink gallons of water here, but no alcohol.

The festival ends with the Diehard Ball at midnight tonight, featuring a solid hour of nonstop dancing.

Down the hall the expert Challenge dancers glide through complicated figures as they learn the flutterby: "Do a flutterwheel, slither, left hand wave . . . finish your flutterwheel before you cast to the right one quarter" . . .

John Wayne would have sat this one out.