They rolled out the tulip beds for Walter Seligmann's 65th birthday yesterday, along with sunshine and a number of other props he has never worked with during a 40-year career in the banqueting department of the Mayflower Hotel. Much to his surprise, the town's newest senior citizen celebrated his seniority at a picnic in Farragut Square.

At noon Seligmann was being escorted to an unspecified restaurant. "About Saltz (the clothing store)." He recounted later, "I looked ahead into the square and saw some familiar faces. Was I surprised!"

The faces were near a large banquet table on the grass in the square's northwest corner. It was set for 20, with white tablecloth, an arrangement of flowers as a centerpiece, two candelabras, silverware and wine glasses. A tuxedoed waiter completed the scene.

Placed as it was, among informally clad, fast-food munching office workers basking in the warm sun, it was a surrealistic anachronism sprung from the mind of a filmmaker. In reality, it had sprung from the mind of Otto Riese, the hotel's catering manager. But passersby who stopped to watch inquired if someone was making a movie.

There were some Hollywood touches. The wine glasses were filled with grape juice lest the Park Service sweep in for a mass arrest. "We've made a spectacle of ourselves," said one of the guests proudly.

Nonetheless, many within the square paid no attention, talking among themselves as they ate or read. Only a few feet from the Mayflower gathering sat a young woman, oblivious. She was reading Tom Robbins' "Another Roadside Atraction."

As for Walter Seligmann, he is no stranger to public celebrations and enjoyed his to the fullest. Between bites of food (fried chicken, cold cuts, ribs with barbecue sauce, salad and fresh fruit compote) he bounced up to talk and to greet friends he spotted passing on the sidewalk.

He reminisced about dinners for heads of state at the hotel and the evening when waiters were dismissed and he alone served a small gathering as then-President Eisenhower briefed them on classified subjects. "I've gone through seven general managers, eight food and beverage managers and four different corporations at the Mayflower," he said, "and they never told me to leave. I guess I did okay."

He will be leaving soon due to mandatory retirement. "I'm really too young," he said. "My health's holding up damned good."

Even in the midst of the party the professional in him prompted an observation on the arrangements as provided by Mother Nature. "I think the only thing missing is air-conditioning," he said.

He was wrong. Also missing was a tool to light birthday candles out of doors. Matches just weren't equal to the task.

But everyone sang "Happy Birthday" anyway and in the French royal tradition of a bygone time bystanders were invited to participate. They let them eat cake.