GARDEN CITY — The 35-story indoor ski mountain would soar over bucolic pine barrens and farms at the twin forks of Long Island.

Developers envision a gleaming $2 billion resort complex, rising out of a Cold War airfield where the Navy once tested fighter jets for “Top Gun” pilots.

But environmentalists are already lining up to fight the ambitious project, which also would feature an indoor water park, a convention center and hotel, a winery, equestrian trails, campgrounds, an artificial lake, and a spa surrounded by botanical gardens.

“Mega-development … could turn rural Calverton into modern-day Orlando,” a recent press release from the Long Island Pine Barrens Society stated.

It’s been a decade since the Navy gave the town of Riverhead — some 75 miles east of New York City — about 6,000 acres of property once used by defense contractor Northrup-Grumman to test F-14s and other aircraft.

Half of the land has already been set aside as a preserve; the other half is designated for development.

Now a group of investors including Scottish home builders, Baldragon Homes Ltd, and real estate developers Bayrock Group LLC, have signed a $163 million deal with the town to transform 750 acres into what they call Riverhead Resorts.

An attorney for the proposed resort, Mitch Pally, tries to emphasize the diverse features of the project, but concedes most of the questions he gets are about the ski dome.

“Americans are very parochial,” he explained. “If we don’t have one in this country, we assume they don’t exist. There are over 50 of them operating in the world today.”

Indeed, from Australia to Scotland to Dubai, ski enthusiasts have been schussing down indoor ski resorts for years.

In America, an indoor ski slope is due to open later this year in the New Jersey Meadowlands, and other projects are in various forms of development outside Atlanta and in Las Vegas and elsewhere.

The project is at the confluence of two popular tourist destinations — the south shore Hamptons and the north shore wine region — that draw big crowds in summer. The developers want the business year-round.

“This has to be a 365-day resort or we’re not making money,” Mr. Pally said. “We have to provide basically the same guest experience in January that we do in July.”

Marketing surveys, he said, have found that 40 million people live within a six-hour drive of the site, and he has designs on the international traveler, as well.

“There are 50 million visitors who go to New York City every year,” Mr. Pally said, applauding Mayor Bloomberg’s tourism push. “As I always say, the mayor’s getting them from Germany to New York. All I got to do is get them from New York to Riverhead.”

But before Mr. Pally starts loading tourists onto the Long Island Railroad for the hour-plus trip from Manhattan, he must get at least 18 regulatory approvals from various government agencies, many of which focus on environmental concerns.

That’s where opponents are gathering for a brawl.The property is considered part of the Pine Barrens of Long Island, 100,000 acres of relatively undeveloped land that sits atop an aquifer system that is the sole natural source of drinking water for the island’s nearly 3 million residents. Because of its critical ecological role, state and local laws limit the type and scope of development in the region.