John A. Hess was dreaming of a week-long holiday yesterday, cruising clear Caribbean waters on a chartered 37-foot sailboat, when an American Airlines employe told him his flight from Washington to St. Croix had been canceled.

Hess, waiting in line at the American ticket counter at Dulles International Airport with many of the flight's 130 other would-be vacationers, had his plans dashed with word that American flight 621, scheduled to depart Dulles at 11:30 a.m., had been grounded by a fuel leak.

With alternate flights already booked to capacity, the holiday turned into an instant hassle for the stranded passangers, many of whom were enraged. Hess saw his $1,300 sailboat charter "slowly evaporating."

"I was standing next to a woman who just couldn't take it," said Hess, a 53-year-old vice president for a Washington-based research and development firm. "She went ape. She kept saying 'I'm not going to take any of this s - - -.' She didn't calm down until the airline spokesman threatened to have her removed."

It was a bleak day for the passengers, many of whom had planned their vacations -- costing thousands of nonrefundable dollars -- several months in advance to avoid the situation they confronted yesterday.

"They've got us planned for a flight to San Juan tomorrow," said Hess. "But that flight is probably overbooked. Then the Prinair flight from San Juan to St. Croix is unconfirmed. We may get there and have to swim to St. Croix."

Chief American Airlines spokesman Art Jackson said the aircraft, a Boeing 707, should have arrived at Dulles from Philadelphia at 11 a.m., but "developed a fuel leak on a ferry flight from San Juan to Philadelphia and was forced to land in San Juan. It's just out of service."

No substitute plane was immediately available, Jackson said.

Several passengers were dismayed to learn they could fly to St. Croix on rescheduled reservations no earlier than Monday or Christmas Day.

"Do you see this?" asked Richard Sugarman, owner of a Washington title company. "This ticket means I can't get to St. Criox until Christmas Eve. I've planned this trip since last July. I understand that the [airline] knew about this cancellation since 8:30 a.m., but I didn't find out until I got here. They [airline personnel] aren't doing anything to correct this."

Airline official Paul Matuozzi, who had just finished walking up and down a line of irritated passengers, handing out all of his business cards, had no comment other than, "we're trying to do our best to reschedule these people."

Some passengers were given the alternative of a "wait and hope" situation for a fully booked 6 a.m. flight to San Juan today. Those passengers would be on standby for last minute cancellations.

"I want to know what American Airlines is going to do right now . . . today about this," demanded Dieter H. von Schramm, North American director for a German trade company, as he copiously scribbled the names and phone numbers of every American Airlines official spokesmen could think of.

"All right then. How about chartering a plane. Can you do that?" von Schramm persisted.

"Sir, that's ridiculous . . . we can't do that. We're sorry. It's an inconvenience, I know," an airline official responded.

"I don't care about the cost of the charter," von Schramm continued, without success. He later added, "This is a $1,400 nonrefundable, prepaid vacation. This airline offers you no protection . . . no protection at all."

Norfolk resident Steve Copeland said he and his friend will lose $107 a day in vacation package hotel accommodations for each day missed.

"I was originally scheduled on a flight that stopped for a changeover in San Juan earlier today. But the airline called me yesterday and said they could put me on the direct flight, the one that's just been canceled. That is terrible."

Bernard Lucas, complete with a white fishing cap decorated with lures, said he had planned a $160-a-day fishing expedition for 10 days.

The Bethesda resident said, "I'm going out of my mind. My new ticket says I'm on a Christmas Day flight. But they aren't going to keep the boat docked just for me."

Airline spokesman Jackson said passengers who chose not to use their tickets would be reinbursed. Round-trip coach fare for the flight was $349 and first-class $577. Actual costs varied depending on when reservations were made or on excursion rates and package deals, an American employe said.

Meanwhile, the Hess family learned its problems were spreading.

Hess and his daughter planned to meet a second daughter flying out of Atlanta at St. Croix yesterday.

"We found out that they [his daughter] lost all their luggage," said Hess, returning from an airport phone. "They're sitting on the boat with only the shirts on their backs. They can't use the boat because I was supposed to be the skipper. They don't know how to drive it.

"I don't have much faith that we'll be getting there tomorrow, either," Hess said.