Ford Motor Co. and New York Gov. George E. Pataki say the number of low-pollution, natural gas taxi cabs in New York City may quadruple under a cash-incentive program to encourage new sales or the conversions of gasoline-powered cars.

The state and Ford are offering a $6,000 cash incentive that will allow city cab operators to purchase natural gas Crown Victorias for the same price as regular, gas-powered ones. Operators also can get $5,000 to convert their gasoline-powered cab to natural gas.About 150 of the 12,000 cabs already on New York City streets are natural gas vehicles. The state and Ford are hoping to add up to 600 with the incentive program.