An estimated 400 to 500 sodden die-hard Apple (AAPL) loyalists waited under umbrellas up to three and a half hours outside the company’s flagship Fifth Avenue store for a chance to buy OS X Leopard on its first day of sale.

By the time the doors opened at 6:01 p.m. the line stretched — in places four or five deep — down Fifth Avenue, across 58th Street and all the way to Madison Avenue.

The rain-soaked customers were greeted in full pep-rally style by black-shirted employees who shouted and clapped as the crowd tramped down the glass-enclosed spiral staircase — and then gave them high-fives as they emerged a few minutes later brandishing their shrink-wrapped packages.

First in line was Bob Greenlees, 23, a student at the Cardozo School of Law. He had been waiting since 2:30 in the afternoon and was still as cheerful and excited as a child on Christmas morning.

“I missed the iPhone line because I was in Paris on my honeymoon,” he said, minutes before the doors opened. “But I watched the webcast.”

“That’s my crazy husband,” said Laura Greenlees, who waited outside with Bob’s computer backpack while he completed the purchase. He came out 15 minutes later with a free T-shirt and a $199 Leopard family pack that he said he would share with his wife and his parents.

The store, which is open 24 hours a day, was expected to have sufficient copies of Leopard to supply all comers — but not necessarily T-shirts. Apple had only stockpiled enough for the first 500 customers.

See also The Day of the Leopard and Leopard: The Reviews Are In