Horseradish, the caviar of masochists.

When it's hot, it's hot. And when it's really hot , it may live up to it eye-watering reputation as the "bitter herb" traditionally served at Passover.

Yesterday, the first night of Passover, Jewish families sat down for seder dinner and nibbled it, as custom dictates, along with a number foods symbolic of their ancestors' bondage in Egypt 3,000 years ago. It'meant to be a serious occasion.

But when it comes time to spread the grated horseradish between slices of matzoh, the celebration can get downright comic. Often, children will start to giggle. "I double dog dare you to eat it!" The parents will start to frown - it's their duty to eat it. And everyone will glance nervously about the table to see who will be first. Finally, the most courageous will take custom to the hilt, hold the nose, close the eyes and bite into the dread horseradish sandwich.

And if it's hot and comes from a jar, it will be a good bet that the horseradish that makes them cry will be named Tulkoff.

"We've got to make people cry for our money," deadpans Martin Tulkoff, 44, a tall man with a long, sad face who is vice president of one of the largest horseradish processors in the country - Tulkoff's of Baltimore."We're in a crying business."

Indeed, customers my weep, but the Tulkoffs only cry on the way to the bank. "We've got 12 Cadillacs parked in back of the plant," boasts Harry Tulkoff, 80, the patriarch who started the horseradish dynasty in 1926 from the back of an East, baltimore produce cat. "My wife has a mink coat made out of horseradish. The bank would never bounce our check, even if it was for a million dollars."

Tulkoff's success - $2 million worth of horseradish a year sold to wholesalers, distributors, airlines, restaurant chains and insitutions - began with Harry's ability to convince people with no taste for the stuff how to acquire one.

He gave it away, door to door. He pushed it on restaurants. He published books of recipes that called for horseradish. He strolled the boardwalk at Atlantic City and offered all comers $20 bills for a dime. When they scoffed, Harry gave them a free daisy - and a bottle of horseradish.

At food conventions, Harry saw to it that everyone who passed Tulkoff's smorgasbord got a taste. Sultry women in bikinis dolloped cold cuts with the latest horseradish incarnation.

"You geo to strike while the iron is hot," says Harry, a Russian immigrant who left the dairy business in New York in 1925 to sell vegetables in Baltimore. "If you buy 500 cases, we give you a color TV. No charge. You want a watch, we give you a watch. A radio? You got it, We used to give away silver dollars."

Nowadays, Harry winters in Miami Beach with his wife. But two sons - Sol, president and head of sales, vice-president Martin - chief of production son-in-law Dan Kishter and their wives and children have taken up the hustle where he left off.

Sol, 57, who once stumped panelists on "Waht's My Line" and at conventions, not rides herd over the bikinis and parades shamelessly about in an imitation tiger-skin jacket to promote Tiger Sauce, a ticklish horseradish-mayonaise blend.

"Everyone calls me, "Mr. Horseradish," he says, opening a tightly packed bottle and turning it upside down. Nothing spills. "Who can beat that?" he asks. "We're top banana in this business."

In the early days, Tulkoff's developed a special "chill-mill" process - grinding and mixing the root at low temperatures and vacuum sealing it in glass jars - to give horseradish a shelf life of six months to a year. After that, it doesn't go bad, it just won't bring tears to your eyes.

And the only way to tell if horseradish will make you cry is to taste it. It begins to lose its zing when grated and mixed with vinegar.

Ex-salesman Kishter, 55, used to stake out supermarkets with gallon jars of the stuff. He would set them in display bins, unscrew the top, prop up the sign - "Sniff this!" - and watch the curious bend noses towards the jar. Grown men wept.

"It knocked their socks off," chuckles Kishter. "There'd always be some wiseacre who took a whiff. They didn't know what hit them."

"We've romanced it and advanced it," says Martin, who invented the machinery used to wash, shred, blend and bottle various Tulkoff products concocted behind locked doors of 22 buildings at East Lombard Street and Horseradish Lane.

The process beings when Tulkoff's sells starter roots to farmers, promising to purchase their crop at the market price. It's a tough crop to raise - the root is sterile and must be sprouted from cuttings - but an acre can gross $2,000, about 10 times what farmers get for corn.

Luther Burbank once offered a $1,000 reward for an ounce of horseradish seeds, but no one ever claimed it.

Planted one spring and harvested the next, the roots are carted to Tulkoff warehouses, where two years' supply is kept crunch and mix about 40,000 pounds a week. Sales are up, they say. Fast-food chains have begun to favor the root as a flavoring.

Harmless until cut, its fumes are said to have given more than one Verdun veteran flashbacks of dread mustard gas. On a rainy day, the aroma hangs in the air, hovering over nearby housing projects, delis and cheap clothing stores like a giant onion cloud. On Tulkoff's assembly line, there is only an occassional sniffle.The plant is well-vented.

"Our neighbors do more crying than we do," says Kishter.

With side-shoot tentacles attached, the whole root looks like an octopus. Trimmed, it resembles a gnarled club. Purists buy it whole at about $1.25 a pound, fearlessly grate it, add vinegar and make their own sauce.

For tart-tongues gourmets, it's derigeur to dab it on roast beef or tongue, to consecrate oysters with it, to blend it with ketchup and baptize shrimp in it, to mix it with mayonnaise and use it on fish. Some bartenders shun Tabasco and stir a teaspoon into Bloody Marys. That's two calories' worth.

At Passover, when the root is eaten with matzoh, gefilte fish and horosis - a tasty mixture of apples, cinammon and nuts that symbolizes the mortar Hebrew slaves mixed into bricks to build the pyramids - the Tulkoff's make sure their horseradish is kosher.

Only the most trusted employes, family members and Rabbi Jacob Max, who inspects the products bottled for Pass-over to insure that preparation conforms to ancient dietary law, are allowed in the mixing room.

Recently, a reporter was denied a full tour of the plant, as the Tulkoffs are very secretive about the business.

But even Tulkoff's has their Deep Throat.

At Apssover, they steam-clean the equipment, switch from grain to a more expensive apple cider vinegar and order employes not to eat in the building. Product contact with anything containing yeast - like a bologna on white, or the grain vinegar normally used to make the bledns - is against dietary law.

Before fleeing Egypt, Moses ordered the Jews to bake their bread without yeast. They didn't have time to wait around for it to rise.

Orthodox Jews grate their own horseradish or put a dent in the 100,000 pounds of the kosher stuff that the Tulkoff's process for delicatessen and supermarket shelves the month before Passover.

Tulkoff's and other processors cut their own deals for the crop. One rival, Silver Springs Gardens of Eau Claire, Wis., grows their own.

Last year, processors imported almost 1 million pounds (about seven percent of the U.S. output), mostly from Canada. The West Germans bowed out of the export game a while back, but their ancestors found horseradish growing wild along the coasts of Europe and named it "Meereetich," or sea radish. Since "meer" sounded like cmare" - horse in English - it came to be known as horseradish.

"Most people think horseradish has to do with horses," says Sol, a short, jowly man in gray pants and a plaid jacket who grins as he flips the sales chart he uses to educate clients. "That's a misnomer."

"We call it 'Jewish Dristan." CAPTION: Picture, Sol Tulkoff promoting Tiger Sauce, by James M. Thresher - The Washington Post