While the mystery man sat plugged into his headset and the biorhythm lady computed her lucky line, 60-year-old Eloise Bell dreamed aloud an Atlantic City fantasy. She was talking sand and surf.

"Never mind the beautiful scenery, how's the payoff?" said Bell, perched in the front seat of the Gambler's Special, an early morning bus speeding her from the suburban calm of Springfield, Va., to a Jersey casino and an afternoon date with a one-armed bandit.

The gambler's special is not a coach for high rollers. The customers who line up every morning in front of District and suburban hotels are strictly from bingo. But for just $19.75 round trip -- and that doesn't include a kickback to each customer from the casinos of $8 in quarters and a box of salt water taffy -- the weekday retinue of housewives, government workers playing hooky, and white-haired retirees figure they can afford the gamble. Especially when the jackpot is just a longshot away.

"We're going after the big one," said Bell with avarice in her eyes. She and her husband Erbin were the veteran gamblers on a recent weekday bus that started in Springfield at 8 a.m. and pulled into Atlantic City 4 1/2 hours and three stops later with 26 passengers.

Riding with the Bells were their son Doug, who works for the Pentagon, and his wife Lee Anne, a group of 10 female slot machine junkies from Delaware and one Virginia couple along for the view.

"We're not gamblers," confided Bob Sparkman, a television salesman at Springfield Mall, escaping for a day of boardwalking with his wife Elsie. "I might put down a two-dollar bet somewhere before the day is over, but mostly we'll just watch."

While the bus rolled over parkways and turnpikes, Phoebe Lucas, the owner of a Delaware hair salon and a short-cut biorhythm chart, looked for promising patterns among her fellow passengers. The mystery man, a round-faced serene sort, kept his head under earphones plugged into a cassette player. Aisle mates exchanged stories about past vists to Atlantic City, when horses drove off steel piers and the only competition for the beach and boardwalk were teen-aged Italian crooners named Sinatra and Avalon.

By the time the bus unloaded at Resorts International Casino, one of the four gambling palaces opened in the last two years, the passengers shared an unspoken camaraderie. All, that is, except the mystery man, who hurried away from the rest of the group toward the boardwalk.

"He's the IRS agent they send with every bus," cackled one women, ignoring the sunshine and the distant sound of surf as she plunged into an already crowded casino.

Most of the midday gamblers were elderly bus riders. The great majority of them jockeyed for position in front of slot machines that dominated a casino floor the size of two football fields.

"The bus crowd are small-time gamblers. Slot machine players. Two dollars a bet," said Phil Wechsler, the public relations director for Resorts, which was the first casino to open in May of 1978. Like other casinos, Resorts depends upon a network of private bus companies within a 200-mile radius of Atlantic City to bring in the weekday crowd at cut rate prices.

"They're small-time gamblers . . . but we want them here," said Wechsler, who predicted that more than 600,000 peoople will ride gambling buses to his Resorts casino by the end of the year. Washington area customers are ferried by East Coast Parlor Car Tours, a 35-year-old District bus company.

But East Coast does not have a lock on the low roller trade. Capitol Trailways of Washington operates daily trips from the District to a second casino. And this week Gray Line Tours of Washington begins its own day trip service from the metropolitan area to a third.

Casino executives are betting that as Atlantic City becomes more like Las Vegas, it will create a new suburban clientele. Local bus companies, meanwhile, are busy staking out claims in those still virgin territories.

"Business will probably be light for a while," said East Coast president Bill Bell about two new suburban Virginia routes started this month. "But we're confident it will pick up."

Gray Line, which began its own Virginia-to-Atlantic-City service this week, will be competing directly with East Coast for what is still only a trickle of day trippers. Neither side will admit of being worried about the competition.

"I think the better (bus company) will come out on top," said Gray Line salesman Derick Neubert, tossing out a challenge.

Passengers on last week's gamblers special were less interested in bus company fortunes than their own. Before the bus had come to a complete stop beside the casino, the driver was being ordered to open his doors.

Not all the gamblers were oozing optimism. Eighty-one-year-old Elva Heywood and her baby sister, 75-year-old Mabel Pleasanton, refused to let hope override hard-earned wisdom.

"We've played a lot of bingo," said Heywood. "You can't beat the house."

Despite their professed pessimism, however, the sisters from Delaware were not left behind when their busmates made the 40-yard hike from parking lot to casino with the speed of jaywalkers avoiding an oncoming truck.

Once inside, however, it took some time to begin losing money. Almost every slot machine had its human mate. Crowds were two deep at the dice tables and the only blackjack dealers who looked lonely were at tables with a $10 minimum bet.

While their wives went off in search of a ripe slot machine, Erbin Bell and his son Doug found a dice table with an opening along the green felt betting edge. The elder Bell, dressed in a white shirt and tie, began placing two-dollar wagers with all the outward expression of man playing a game of chess against himself. After he had won a few rolls, his son sidled up to the table to place some cautious bets beside him.

Charlene Cristofori was the first to milk a slot machine for a decent payoff. Twenty minutes after leaving the bus, the Delawarean stood before a multi-colored machine that rang like a fire alarm and spit out $50 in silver dollars.

"That wasn't hard," said Cristofori.

Halfway down another row of machines, Phoebe Lucas, the biorhythm lady, was having a tougher time. Standing between a pair of dollar slots, Lucas looked to be performing a chore. Feed and crank. Feed and crank.

"I've done better," said Lucas grimly.

The backdrop to all of the individual absorption was a collective hum of jingling coins and upbeat lounge music, punctuated occasionally by a winner's yelp or a loser's groan. The walls were blood red. The low black ceiling was studded with spotlights which seemed to create cones of swirling smoke. The decor was pure casino.

Except for a short lunch break, most of the bus riders stayed locked into their struggle against the odds. With just six hours to gamble, there no time for the wax museum or a tag game with the surf. One woman from Delaware, Ann Panasewicz, did break away long enough to get her fortune read by Madame Edith inside a boardwalk Temple of Knowledge.

"She told me I was going to make a good investment soon," laughed Panasewicz, who spent most of her afternoon throwing good money after bad.

With few exceptions, the gamblers were separated from their money. Success was measured in the time it took to lose the entire bankroll. Cristofori was the only slot machine player on the bus who claimed to end the day even, and that was due to her early jackpot. The biggest loser left $500 in a variety of cursed machines.

"Losing money is hard work," said one passenger, standing in the aisle of the homebound bus littered with sleeping losers.

Erbin Bell was one of the few gamblers who ended the day a winner.By betting conservatively, walking away from cold dice and maintaining strict self-discipline, Bell said he had tasted victory.

"I won enough to buy a hamburger," said Bell, still sharp in his white shirt and tie. His wife was equally composed, but hers was a loser's stoicism.

As the bus left casinoland, the only passengers who seemed completely at peace were Bob and Elsie Sparkman, who spent the entire day on the beach and boardwalk, and the mystery man. While the other gamblers were collapsing into their well-cushioned seats, the mystery man bounded up to the bus carrying a loosely wrapped package and wearing the look of someone who had hit the jackpot.

"I was on my own mission," said the man, who would only identify himself as "Mr. W." Though he had not stepped foot in a casino, his trip had been a gamble of sorts. For the second time in as many weeks, he had taken the bus to bargain for a porcelain organ grinder being sold by a small boardwalk shop. Fifteen minutes before the bus left, said the man, now stripped of mystery, he finally browbeat the owner into selling it for more than $1,000 below the advertised price.

"It's funny," said Mr. W. "These are supposed to be the wheeler-dealers, and I'm the only one to bring back something to show for the trip."

But his gloat proved premature. Before the bus was an hour gone, the low rollers had regained their lost enthusiasm.

"We're gonna play some poker in the back of the bus," announced Jennalea Foraker, one of Delaware's most gracious losers. "But we're gonna play for saltwater taffy. That's all we've got left."