The side of beef sizzles on the spit at Canby's. The tank tops flutter on their racks outside the T-Shirt Factory. The sign of the summer -- "Help Wanted" -- fills the window of every other shop.

Up and down the coast, from Rehoboth to Ocean City and on to Virginia Beach, the restaurants and realtors, lifeguards and shopowners are preparing for Memorial Day weekend -- the official opening of "The Season."

"This is what it's all about," said Dave Canby, 43, owner of Canby's in Rehoboth and purveyor of hundreds of barbecue beef sandwiches on even the stickiest of summer days.

"The Season" traditionally brings crowds and a festive atmosphere to the shore, but, most of all, it brings a transformation.

Virginia Beach, already its state's most populous city with 311,000 people, adds another 50,000 revelers each weekend. Rehoboth blossoms from a quiet well-to-do village of 3,000 to a family haven of 75,000. And Ocean City, that 10-mile-long tribute to fast food and fast times, virtually explodes from a fishing town of 6,000 to a carnival city of 250,000.

During any given week, manager Lloyd Byrd and his staff at Phillips Crab House in Ocean City will sell 300 bushels of crabs. Dinner guests at the Rusty Rudder in Rehoboth will consume several hundred whole steamed lobsters each night. Vacancies will be hard to come by among Virginia Beach's 10,000 hotel and motel rooms.

Because of the mild spring, the crowds arrived earlier than usual this year. Last weekend, the beaches of Rehoboth and Ocean City were covered with sunbathers working on early tans, but only the bold-hearted dared to venture into the 62-degree Atlantic. The shadows of gulls flitted across blankets. The warm breeze carried that patented boardwalk aroma: saltwater, coconut oil, french fries.

"I guess you had to want to go in," said Kate Evans, 17, shivering and combing her wet hair. Kate and other members of her junior class at Unionville High School in Unionville, Pa., drove to Rehoboth after their prom Saturday night.

People go to the beaches for obvious reasons -- to relax, to party, to spend money. Last summer, as usual, they spent millions. In Sussex County, Del., which includes Rehoboth, Bethany and Dewey beaches, the tourist industry generated about $146 million, according to the state tourism office.

In Virginia Beach, the 1984 summer brought in about $295 million -- a 13 percent increase over 1983, said Jim Rickett, the city's tourist development coordinator.

And in Ocean City, town officials said, last summer's tourist industry was a $677 million business.

One of the largest single expenditures for the beachbound tourist is always lodging; room rates traditionally shoot up with the coming of the season. The charge for a double room at the Hobo Beach Motel at Rehoboth, for example, increases from an April low of $34 a night to a June-August high of $70. Weekly rates at the Royal Palm Townhouses in Ocean City are $185 in the off-season, $410 during the peak summer months. Real estate agents say this year's prices are roughly comparable to last year's.

Many beachgoers develop attachments to certain beaches and return there year after year. This season, they'll find a few changes.

Virginia Beach has plans to beautify Atlantic Avenue, its three-mile long oceanfront strip. Six side streets will be closed, creating tree-shaded alcoves with benches and live entertainment. "It's an experimental thing," Rickett said.

Rehoboth has gained its first Mexican restaurant but lost its horse-drawn carriage tour, which had a tryout last summer.

"The horses tied up traffic, so it didn't work," said Sandra Ardis, director of the town's Chamber of Commerce.

Ocean City, with its towering condominiums and cluttered beachfront, has suffered a spiritual loss. This will be the first summer without mayor Harry Kelley, the flamboyant town booster who daily ambled down the three-mile boardwalk, passing out miniature keys to the city. Kelley, who had been mayor for 14 years, died of a heart attack in February.

As always during "The Season," there is a strict, if unwritten, code of what is considered current and cool.

T-shirts, for example.

This year marks the return of the basic crew-neck short sleeve model ($5.99) over the muscle shirts and net-trimmed styles of the past, said Bridget Bartley, manager of the T-Shirt Factory in Rehoboth. What adorns the front of the basic T-shirt, however, is crucial.

"Gumby and the Jetsons are big," said Bartley, naming vintage stars of animation. "Also, the sayings."

The sayings come in big black block letters: "Choose Life." "Choose Beer." "Boy Toy." "Born to Shop."

At Rehoboth, casual observers report, the one-piece suit is the only chic beach apparel for women; female bathers in Ocean City, on the other hand, stubbornly cling to their bikinis.

Seafood in all its variations will remain, naturally, the favored meal, while beach bartenders predict that strawberry daiquiris will again be the preferred mixed drink. Beer, however, is king.

"People come in at the end of the day looking like red lobsters and they want something cold," said Lloyd Byrd of Phillips Crab House.

When asked to describe their particular appeal, however, promoters for Rehoboth, Ocean City, and Virginia Beach alike automatically return to the same line: "We're a family resort."

On a recent afternoon at Ocean City, Bill Kieley and family from Paterson, N.J., bore out that claim. The sun shone strongly, framed by puffy white clouds. On the water, a white boat traced the shoreline, its marquee flashing, "Tugo's Pizza . . . Free Delivery . . . A Lady in Waiting . . . Ocean City's Only Maternity Shop . . . Temperature . . . 72 . . . " Nearby, five teen-age boys chased a football.

Bill Kieley's nose was slick with baby oil. At his side was his year-old grandson, Thomas Kieley, sleeping soundly in a playpen shaded by a striped beach umbrella.

"It's his first trip," said Kieley, "but my wife and I have been coming here for the past 30 years. We like it because of the size of the beach and because it doesn't have the casinos like Atlantic City. A real family place."