They billed the event that brought an estimated 750,000 people to Andrews Air Force Base yesterday as the Joint Services Open House.

The Defense Department might just as easily have called their crowded annual show Beach Party on the Tarmac.

Spectators lay on blankets and under striped umbrellas near the airfield, coolers at their sides. Radios blared. Bodies glistened with suntan lotion. Long lines formed at the hot dog and T-shirt stands.

But while the atmosphere seemed festive and casual, the event was carefully calculated.

"We want the public to see the personnel and the capability of their military," said Lt. Col. Mike Riley, an Andrews spokesman who supplied the crowd estimate.

The annual open houses began in 1976.

Yesterday's crowd came to see the Army's Golden Knights and the 82nd Airborne float down on parachutes from the puffy white clouds. They came to see the military working dogs and the bands, the color ceremonies and the F-15s. But most of all, they came to see the Thunderbird jets fly over them in thrilling, cloud-chasing formation.

"I like that daredevil stuff," said Mike Holland, 23, a bricklayer from Columbia, who was joining several friends in a tailgate beer party. "Spectacular. It makes me wish I was a pilot."

For most people, it was impossible to watch the military extravaganza without a twinge of that feeling called patriotism.

"It's a good feeling," said Denise Burger of Morningside, whose family was having a picnic in the back of their brown pickup truck. "I don't know why, but you feel something when you see those planes and those paratroopers."

"This is good for the relationship between the military and the rest of us," said Martin Lilly, 31, a computer programmer from Hyattsville. He and his wife, Susan, son Martin, 2 1/2, and daughter Julianna, 1, sat on a blanket eating sunflower seeds, eyes trained skyward at the Golden Knights.

Adam Littlefield, 4, wore GI Joe sunglasses and a deep-blue Thunderbird T-shirt he had just wangled out of his dad, Jim, a Gaithersburg accountant. Adam gave his assessment of the day's events.

"Well," he said in a small boy's piping voice. "first, I saw the parachutes. And then I saw the airplanes flying by. I liked the airplanes until they landed, and then I didn't like the noise. The parachutes were quieter."

It was the Thunderbirds, however, that were the clear favorites. Although they appeared a half hour late, the roaring red, white and blue F-16s transformed the crowd. Radios were switched off. People in line at the concession stands began running for a better view. Thousands of people stood motionless, silent, with one arm raised to shield their eyes from the sun.

The jets sliced the sky, skimmed the horizon upside down, then flew off in majestic formation. The crowd was reverent.

"Boy," said Colin Marks, 7, of Forestville. "I didn't know planes could do that. That's why I like them."