NEWARK, N.J. (AP) — A study commissioned by the Port Authority of New York and New Jersey calls for major expansions at John F. Kennedy and Newark Liberty International Airports.The Regional Plan Association also calls for upgrades at LaGuardia Airport, which doesn't have room to expand.Newark and LaGuardia are plagued by low on-time performance.The study, reported by The Star-Ledger of Newark, suggests it will only get worse if nothing is done. The report says demand for travel at the three airports could grow by nearly 50 percent over the next two decades.The report says additional runways should be added at JFK and Newark Liberty and the PATH train should be expanded to Newark Liberty as part of $15 billion in improvement projects.___Information from: The Star-Ledger,