At William B. Fitzgerald's weekly lunches, one may find himself sated next to a prince or plumber, a bank president or small depositor. One thing is more certain: Whatever your state in life, someone quite different is likely to be at the next place.

An invitation to these informal Thursday gatherings limited to eight or 10 has become one of the more coveted tickets in town in the three years they're been held.They take place in a small, elegant dining room in the back of the Connecticut Avenue offices of the Independence Federal Savings and Loan, of which Fitzgerald is president.

Fitzgerald says he wanted to bring together a mix of people for "the betterment of the community . . . people with no link, no chance to sit down and get to know one another. I thought we'd do it about a dozen times. The idea just kept going."

The ranks of luncheon guests have grown to several hundred now, and yesterday it was their turn. More than 300 took Fitzgerald to lunch, at the Madison, and Fitztgerald, being one who has always advocated speaking the truth at his affairs spoke right up and suggested they take him every July.

Yesterday's occasion marked the 10th birthday of Independence, the first integrated savings and loan institution in the city. Fitzgerald, 46, is a Washington who began as a home-insulation mechanic and later built a successful real-estate business.

While no one will say specifically what is said at any of the "Thursday lunches - they are off the record - yesterday's turnout was testimony to Fitzgerald's civic enterprise. The crowd was a typical Fitzgerald mix of the city's government and business leaders, writers and lawyers, blacks and whites, men and woman.

"We have two gentlemen in this room, one of whom will be the next mayor," said Fitzgerald, meaning Sterling Tucker and Marion Barry.

Fitzgerald says his Thursday luncheons are "educational for everybody, and out of them relationships have developed and endured for the betterment of the community. We might have a woman who says she's been denied a loan, and there's a banker sitting there. Because of the luncheons, dozens of businesses have been helped."

Fitgerald says national and international issues are discussed, individual with different views on these issues invited. But the conversation usually gets back to the city.

Of course, the luncheons do nothing to hurt his savings-and-loan business either. But then no one ever said Fitzgerald wasn't a sharp businessman.

"Oh, it helps the business, as a residual," he said. "We do benefit economically. But it wasn't done for that."

Fitzgerald jokingly told his audience yesterday that the luncheon was "just a tryout" for something even bigger, maybe a cruise. "You think you could deal with each other for about a week? Because if you think so we can plan it."

He probably could, too, except as he said. "What would happen to the city?"