The Port Authority of New York and New Jersey today will authorize the purchase of a lease for Stewart International Airport, an agency spokesman confirmed. The 93 years remaining on the lease will be purchased from a British company for $78.5 million, and the Port Authority expects to assume operations in October.

Located near Newburgh, N.Y., 55 miles north of the city, the former Air Force base will be used to relieve traffic at Newark International, La Guardia, and John F. Kennedy International airports. The three airports, which together handled 104 million passengers last year, are functioning at close to peak capacity, and annual traffic is expected to grow to 150 million by 2025.

Stewart International Airport currently services just 300,000 passengers a year; it has the infrastructure to handle 1.5 million passengers annually. Its two runways do not share airspace with the three major airports in the region, and its infrastructure could be expanded to service up to 10 million passengers, the aviation director of the Port Authority of New York and New Jersey, William DeCota, said at a board meeting last month.

“The expansion of Stewart Airport is a critical component of the continued growth of the Hudson Valley,” Governor Spitzer said in a statement. “Stewart International Airport will provide much needed relief for our three major airports.”

Roughly 11 million passengers who currently rely on Newark International, La Guardia, and John F. Kennedy International Airports live in counties north of New York City, a Port Authority spokesman said. JetBlue already flies out of Stewart International Airport.

Stewart International is currently operated by the National Express Corporation, a British transportation company, and the New York State Department of Transportation. The Port Authority has been actively looking to purchase a fourth airport for more than a year.