Paul Idomir of Beltsville deposited three $1 tokens into the slot machine that had become his obsession, pulled the arm and stared transfixed as the symbols flashed in front of him. The machine said: 7 7 7 7. . .

One more 7 would change his life. "Those first four sevens came down plunk-plunk-plunk-plunk," Idomir said. "My eyes kept getting wider and wider. It seemed like that last wheel must have spun five minutes." Suddenly, a bell started ringing, security guards started running across the floor of Las Vegas' Flamingo Hilton Hotel, people were yelling. Idomir kept staring in utter amazement:

7 7 7 7 7.

He had just won $370,000, the largest slot-machine payoff in history. It was a payoff for what Idomir would say was hope and faith, but which others might describe as a sick, destructive, costly compulsion.

Idomir's business is television sales and services, but gambling has been his preoccupation. He started betting the horses at Laurel Race Course in 1954, and soon began making excursions to Las Vegas, where he mostly shot dice and played blackjack. He lost at everything. But it was not until one day last August that he developed his most virulent case of gambling fever. He became hooked on slot machines.

Many Vegas casinos feature "progressive slots" that typically take $1 tokens and produce mammoth jackpots. Four or five wheels spin so that symbols appear on three horizontal lines. Different combinations produce different payoffs; three bells in a row might be worth $18. But the jackpot is paid only when the player has deposited $3 and the proper symbols have appeared on the bottom line, the "third coin line." The winning symbols vary; on some machines there may be four bars; on others, five 7s.

At the Hilton, several machines will be grouped together on one "carousel," with the jackpot for any of them starting at $100,000. Every time a player deposits $1, the size of the jackpot grows by a nickel, up to a maximum figure. A lot of dollars pass through those machines.

Last August, Idomir was on his way to the blackjack tables when he passed by a progressive slot carousel where the winning combination was four bars and the jackpot was $320,000. He had a few loose coins in his pocket, so he played and watched as three bars appeared on the bottom line, followed by a fourth bar that cruelly stopped on the middle line. He had been so close!

For the next 22 hours, Idomir stood there and fed coins into the same machine, sustaining himself on coffee and cigarettes, pulling the arm of the one-armed bandit until his palm was almost raw. He ran out of energy and money almost simultaneously, and quit after losing nearly $1,000.

Two hours later, somebody dropped three coins into Idomir's machine and won $320,000.

He was still preoccupied by the slot machines when he returned to Las Vegas last Christmas. "For years," he said, "I'd been losing and losing at just about everything. I said, 'Hey, I'm going to take this one big shot. If I do win, I'm going to win big and get back all I've lost.' I took just about everything I owned."

Of course, the inescapable precentages of casino gambling ground him down over the next several months. "I went back and forth from Vegas to Washington a number of times, looking for fresh money," Idomir said. "I borrowed from friends, relatives, banks. I'm in hock to everyone." When he started playing the slot machine at the Flamingo early Sunday evening, Idomir estimated that he had lost somewhere between $20,000 and $30,000 in his pursuit of the one big score.

Earlier that morning, a player had hit a $365,000 jackpot on another carousel of machines at the Flamingo, and Idomir said, "The pattern has been that lightning strikes in a day or two. I had a feeling that this might be my day." Of course, he had had that same feeling many times before. He bought $100 worth of coins, went through them, and lightning didn't strike. He had just started going through his second $100 worth when the 7 7 7 7 7 came up and, Idomir said, "I felt like I found the pot of gold at the end of the rainbow."

The next day, the Flamingo held a press conference at which Idomir was presented a check for $370,000. "We're going to have a heck of craps game tonight!" he exclaimed.

However, he did not have a heck of a craps game. He has not gambled a penny since he hit his jackpot. After devoting all his thoughts and his fantasies and his energy to his pursuit of the one great score, he wasn't quite sure what to do with his life now that he had made it.

"I sure don't feel like fixing any more tV sets," he said. "But where do I go from here?"

Instead of indulging more of his fantasies and pushing stacks of $100 chips across the craps tables at the Flamingo, Paul Idomir went to the dentist yesterday and had a root canal. Presumably, he was feeling no pain.