Long Island is increasingly becoming a region of economic extremes, with a shrinking middle class.

That deeply troubling trend shows no sign of abating. Unless it does, the divide will grow deeper, marginalizing the very people who have come to define the region’s history and are essential to its identity and economic vitality.

This is a pivotal moment for the Island.

There is still time to stop the bleeding and shift the trends, but it will take true leadership from those in government, business, academia and community organizations. It will take a willingness to change and to focus on developing industries of the future, as well as new housing options, including rentals, and improved mass transit.

The disturbing shift in the region’s economic makeup was put into focus by the Long Island Association. Using Census Bureau data, the business group’s Research Institute released a study finding that just 57.8 percent of Long Island households fit into the middle-class brackets of earning between $46,165 and $184,637. In 1990, based on incomes then, 66.9 percent fit the middle-class description.

There are problems with the definition. If you earn $50,000, you’re considered middle class, but many don’t feel like it when Nassau County’s median monthly housing cost is $2,185, which would eat up more than half of that annual income. And many earning $185,000 on the Island don’t consider themselves upper class. But whatever the definition, the problem is obvious. It’s partly demographics, as the region ages and earns less; partly that those still working could buy more in areas with lower costs; and partly that some people have grown richer while others are poorer. But whatever the reasons, we know that a strong housing market and consumer spending — backbones of our economic growth — are fueled by a strong middle class. An economy without that all-important center isn’t sustainable.

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So, to start, we need to control property taxes. In addition, there’s an opportunity to transform the region in larger ways. At the heart of that is the plan pushed by regional advocates and local officials to create a biotechnology and medical research corridor, a massive effort encompassing academic activity at our universities like Stony Brook and Hofstra, scientific research at our prominent laboratories in Brookhaven and Cold Spring Harbor, and business growth at the Ronkonkoma and Nassau hubs.

If it succeeds, the initiative, which was promised $331 million in state funds last spring, could transform Long Island into a place where a young middle class could thrive. We’ve been talking about biotech clusters and new industry development for decades, and it has failed to come together. This time, it could work.

There’s more. Long Island has to keep fighting to build more housing near transit hubs, including a mix that is truly affordable. Better Long Island Rail Road connections to New York City are key.

There’s a lot to do, but there’s also a lot at stake. If the efforts work, 30 years from now, we’ll be celebrating a growing middle class, a thriving economy and a regional success story. — The editorial board