The New York region’s two largest airports, already choked with crowds and delays, may need to be radically reconfigured so they can make way for vitally needed additional runways that would help accommodate a projected increase of almost 50 million air travelers per year within two or three decades, according to a new study.

The study, from the Regional Plan Association, calls for as much as $15 billion to be spent at Kennedy and Newark Liberty International Airports. At Newark, all three terminals would have to be at least partially razed, then rebuilt; at Kennedy, part of Jamaica Bay might have to be filled to create space for one or more new runways.

The proposed expansions would amount to the most ambitious reshaping of any of the region’s major airports in several decades. They would require significant changes in the region’s airspace, a modernization of the system for controlling air traffic and at least one act of Congress.

If the proposals are accepted by the Port Authority of New York and New Jersey, which operates Kennedy, Newark and La Guardia Airports, they would surely encounter stiff resistance from local and national advocates for the environment, the report admits. They would also have to survive the political tug of war between the governors of New York and New Jersey, who jointly control the Port Authority.