NEW YORK -- The Port Authority is planning to buy the operating lease of Stewart Airport, setting the stage for the facility to become the fourth major airport in the Tri-State area.

According to the terms of the deal, the Port Authority would pay $78.5 million to acquire the 93 years remaining on the lease currently held by the National Express Corporation. The lease expires March 31, 2099.

In 2006, 300,000 passengers passed through Stewart airport, which covers 2,400 acres of land in Newburgh, N.Y. In comparison, New York City's LaGuardia Airport is 680 acres.

Authorities believe the airport could accommodate up to 1.5 million passengers annually.

The Port Authority is making the move because it fears the region's three major airports --LaGuardia, John F. Kennedy and Newark Liberty -- will reach operating capacity in coming years, with no room to expand.