They come in droves, the waltzing grandpas and twisting teenyboppers. Every weekend they don their bouffants and spiked heels, their shags and faded denims - all for an evening of polka dancing at Max Blob's Park outside Jessup, Md.

Since 1933 the crowds have shown up at this oversized beer garden for pitchers of dark brew, a six-man polka band and a dance floor the size of a baseball field. On a good night, a thousand flock to Blob's: regulars driving in from New York and West Virginia and visitors from as far away as Austria and Czechoslovakia.

Some have been known to camp out in the parking lot during special celebrations. This Sunday is one of them, when Blob's holds its annual Sonnenwend Feier, a party in honor of the longest day of the year. Starting at 2 o'clock, the fest features a lineup of German bands, Bavarian folk dancers and enough bratwurst to fuel an army of polka dancers. At night the revelers build a spectacular bonfire, inviting everyone to jump through the flames for good luck.

Actually, the hoopla on a normal night at Blob's isn't much different. There are always crepe streamers and paper globes hanging above the rows of red-draped tables. The peppery house band, Joe and the Rheinlanders, oompahs its way through a repertoire of waltzes, polkas, jitterbugs and disco tunes for the young at heart. The dance floor is forever jammed with the superskilled and the slow-of-foot, though no one cares too much about style.

When the music begins, people seem more interested in dashing for the piece of open space to bounce and twirl to the hop-and-step rhythms. Blob's regulars already know the classic fandangos like the Silver Slipper, the Paul Jones and the Bumpsy-Daisey. Those who don't hail from Bavaria improvise with modern steps to create a sort of polka-jitterbug or polka-bump. Or you can ask your waitress to dance, because she'd usually love to.

Max Blob wanted it that way. Forty-five years ago young Maximilian decided to transform his vegetable farm into a gathering place for people from the Old Country. He built a small frame building on his land to hold a bowling alley and a few tables. And every Sunday he brought a truckload of German friends from Baltimore to treat them to homebrewed beer, live music and hearty German food.

The outings became famous and made "Onkel Max" a patriarch within Baltimore's immigrant community. It wasn't long before popular demand prompted Blob to go public and expand his dancing space and party hours to include Friday and Saturday nights. With a 10-cent entrance fee for many years, Blob's became the social hub for thousands of first-generation Americans.

Nowadays that tradition has grown to include a mix of second- and third-generation Germans, Poles, Puerto Ricans, Spaniards and youth-culture immigrants from Baltimore and Washington. A dollar at the door brings you inside the stucco building decorated with blue-and-white Bavarian flags predating World War I. You can buy pitchers of wine and beer for $4 or order house specialties like sauerbraten and wiener schnitzel for $4.50.

But most people come for the dancing. Hefty women with jewelry and polyester pants suits spin their husbands and sisters or girlfriends. Long-haired college students in tee-shirts and sneakers away with each other in a polka fever. Waitresses dance with other waitresses. One youg woman was seen dancing with her year-old baby clutched to her bosom.

"The same people have been coming back every Saturday and Sunday for years," says Ann Eggerl, a grand-niece of Max Blob who works as a waitress. When Onkle Max died several years ago at the age of 84, the business went to his niece and nephew and others in the family. Among the current kin serving tables are several cousins, two sisters-in-law, an aunt and uncle, plus two brothers behind the bar.

The family operation has done much to save Blob's from melting-pot Americans. You won't find any golden arches at the door of Blob's; rather, a sign in German that translates to "Welcome from the heart." People come here to celebrate 75th birthdays and 30th wedding anniversaries. Joe and the Rheinlanders don't mind dedicating a song to a new college graduate or annou cing a "Ladies' Choice" just as tehy used to at the teen hops in suburbia.

"Blob's doesn't have a nightclub atmosphere," remarks jean Heuther, a Baltimore receptionist who's been attending the dances for five years. "Nobody cares how you look or dress. And none of the girls are afraid to talk to the guys."

Granted it's not all Lawrence Welk classics on the dance floor.During the band breaks, a jukebox is wheeled out for the teenage girls who would rather hustle than clinch in the polka. Line dances attract students of all ages, while you can watch the novices counting time. "One-two-three-kick, forward-jump-kick-twirl." Kibbitzers in the audience call out the steps in case someone starts to falter.

Other patrons mingle over glasses and buy beer for each other at a furious pace. There's a lot of chatter and jokes concerning - what else? - the dancing and dancers. Local politics and Orioles' baseball scores are other popular topics. The social hodgepodge at Blob's rarely creates barriers, at least none that can't be broken down by a polka reel. As one feverish dancer lamented: "It's only sad that we Italians don't have anything like Blob's.