NEW YORK - New York City officials are studying a proposal to extend the No. 7 subway line from Manhattan under the Hudson River to Secaucus after New Jersey Gov. Chris Christie killed plans for a tunnel linking the states. Mayor Michael Bloomberg's administration said the subway plan would double commuter capacity and spur regional economic growth. Christie on Oct. 27 canceled the train tunnel, saying New Jersey couldn't afford as much as $5 billion in potential overruns on the $8.7 billion initial cost of the project. Running the subway line from Manhattan's far west side to a rail station in Secaucus might reduce the project's cost to about $5.3 billion, officials said. It also promises billions of dollars in new jobs and increased home values by linking Manhattan and Long Island City, Queens, with the New Jersey suburbs, proponents said. 'Extending the 7 line to New Jersey could address many of the region's transportation-capacity issues at a fraction of the original tunnel's cost, but the idea is still in its earliest stages,' said Andrew Brent, a spokesman for Deputy Mayor for Economic Development Robert Steel. The line is undergoing an extension from its current run from Flushing, Queens, to Times Square, with a planned terminus at 34th Street and 11th Avenue. The original goal of the $2.1 billion, city-funded extension was to open Manhattan's far west side to development. Rezoning and future growth in midtown Manhattan's office market may add 30 million square feet of space with 120,000 new workers in the next 30 years, according to an Economic Development Corp. memo obtained from a person familiar with its details, who declined to speak publicly before it is released. The area on the far west side, called Hudson Yards, was described by Bloomberg administration officials as Manhattan's last underdeveloped neighborhood. Joanna Rose, a spokeswoman for Related Cos., the chief developer of office towers, apartment buildings and cultural amenities planned for the area, declined to comment on the plan. The already completed tunnel work under Manhattan would drive down the cost of extending it across the river, planners say. It would also eliminate $4 billion required for property acquisition in the original New Jersey rail plan, dubbed ARC, an acronym for Access to the Region's Core. 'As the governor indicated when he ended ARC, he's open to new ideas to resolve the trans-Hudson transportation dilemma,' said Michael Drewniak, a spokesman for Christie. 'But any plan that is first feasible would need to be fair and equitable to New Jersey in that all jurisdictions benefitting from the tunnel would share the costs appropriately.' The plan's benefits include that it delivers the 'same capacity as ARC for half the cost,' 'facilitates economic growth' and 'provides infrastructure we can afford,' the Economic Development Corp. memo states. It also has the added advantages of avoiding the already overcrowded Penn Station at a time when officials expect ridership from New Jersey to increase to 62,000 from 39,000 per day over the next three decades, the memo said. New Jersey's northern suburbs may be the major suburban growth area in the region, with a projected 1.36 million population increase by 2035, the memo stated, citing studies by the New York Metropolitan Transportation Council, an organization of regional governments that works to coordinate how transit should be financed. Christie's killing of the ARC project means the state may have to repay the U.S. government $350 million already spent on the project, forgo $3 billion in additional federal aid and lose 3,000 construction-worker jobs federal and Port Authority officials said the tunnel would generate for the next decade. It also may have cost New York and New Jersey 44,000 jobs and $4 billion in additional income that would have come through economic growth, according to a 2008 study by New Jersey Transit. The mayor is founder and majority owner of Bloomberg News parent Bloomberg LP. --With assistance from Dunstan McNichol in Trenton, N.J., and David Levitt in New York. 