Southampton, N.Y. ? Hamptons hoi polloi probably assumed it was always No. 1.

Coopers Beach, with pristine white sand gently sloping toward a shoreline of lapping waves, convenient parking and amenities and nary a gum wrapper in sight, has been selected as America’s best beach in an annual survey released today to coincide with the start of the summer vacation season.

“New York has world-class beaches, but I don’t think a lot of people in the United States know about them,” said Dr. Stephen Leatherman, director of Florida International University’s Laboratory for Coastal Research. Known by the moniker Dr. Beach, this is Leatherman’s 20th year of compiling a list of the country’s top 10.

This year’s list includes two beaches in Florida, and Leatherman said he was not worried about pollution from the oil spill affecting those locations. Siesta Beach in Sarasota took the No. 2 spot on the list, and Cape Florida State Park in Key Biscayne was No. 10.

He said Cape Florida, on the southeast coast, “doesn’t get the wave activity” that can lead to tar balls washing up. As for Siesta Beach, he said he had looked at currents and believes “there’s very low probability the oil will get to southwest Florida.”

Leatherman’s list also features another New York beach, Main Beach in East Hampton, Long Island, not far from Southampton. Main Beach takes the No. 5 spot on this year’s survey.

“When most people think of a beach vacation destination, they go south,” Leatherman said. “I kind of think the east end of Long Island is a well-kept secret for most Americans.”

Rounding out the top 10 are Coronado Beach, Calif. (3), Cape Hatteras, N.C. (4), Kahanamoku Beach in Waikiki, Honololu (No. 6), Coast Guard Beach in Cape Cod, Mass. (7), Beachwalker Park in Kiawah Island, S.C. (8), and Hamoa Beach in Maui, Hawaii (9).

Coopers Beach has been a contender for the top spot in recent years, but this is the first time a New York beach has made it to No. 1, Leatherman said. He considers factors like water quality and temperature, cleanliness, weather, sand, safety and facilities in making his list.

Once a beach makes it to the top spot, it is retired from consideration in future years, he said. Leatherman added that designation as the country’s No. 1 beach usually brings as much as a 20 percent bump in tourism.

“Both Main and Coopers beaches have been recognized in the past as being among the top 10 beaches in the country — and to now hold the top spot is especially significant when you consider the quality of the company we’re in,” Moke McGowan, president of the Long Island Convention & Visitors Bureau, said in a statement.

Main Beach was in the headlines in April after a 13-ton baby whale washed ashore and had to be euthanized; thousands of onlookers visited the ailing mammal on the seashore while it struggled for life over several days.

Several miles away on Coopers Beach, locals trying to get a jump on summer spoke about the cleanliness of the beach and described it as a welcoming, family-oriented playground.

“It’s wide, the sand is like baby powder,” said Carol Gerbereux, a visitor for at least 40 years. “It’s just a beautiful location; it has wonderful facilities and it’s just a pleasure to come here.”