“It is alarming that he would spring a new project on people without explaining how to pay for the old projects,” said Nicole Gelinas, a senior fellow at the Manhattan Institute. “Are we going to keep up with the Second Avenue subway, never mind a new project?”

For La Guardia’s passengers, any doubts may be outweighed by the potential convenience. A survey by the Port Authority in 2008 showed that 75 percent of travelers from Manhattan used a taxi or car service to reach the airport; only 16 percent rode buses or shared a van.

The governor’s office gave no estimate for how long it would take passengers to ride from Manhattan to La Guardia via the proposed station, which is farther east of Manhattan than the airport.

Proposals for a train to La Guardia have circulated in transportation circles for decades. Other ideas have included a transit link from Woodside, Queens, or extending the N subway line from Astoria to the airport, a plan promoted by the Giuliani administration but felled by Queens politicians concerned about its effect on local neighborhoods.

By comparison, Mr. Cuomo’s proposal is cheaper and less intrusive to residents, according to Elliot G. Sander, chairman of the Regional Plan Association, a group that advises on infrastructure planning in the New York area.

Image Mr. Cuomo said his office needed “a couple of months to work up the design” of the elevated AirTrain before a timetable could be decided. Credit... Ruth Fremson/The New York Times

“It is relatively simple, relatively inexpensive and has minimal impact on the surrounding community,” said Mr. Sander, a lifelong resident of Queens. “You’re not doing underground tunneling. It’s a simple, short connection.”