NEW YORK (AP) _ Mobil Corp. is expanding its computerized debit-card sales of gasoline, related products and services into the New York metropolitan area under an agreement announced Tuesday with Citibank.

More than 1.5 million Citibank customers in New York, New Jersey and Connecticut will be able to use their Citicard bank cards for purchases at specially equipped Mobil stations around the country beginning early next year.

Unlike a credit card transaction, in which a customer is billed later for his purchase, the amount of a debit-card purchase is electronically deducted from a customer's bank account at the time of the sale.

Because the purchase is akin to a cash transaction, debit card users are entitled to Mobil's 4-cent-a-gallon discount for cash payments on gasoline sales.

Mobil now has about 1,400 stations equipped for debit-card sales in Arizona, California, Florida, Maryland, Oregon, Texas, Virginia and Washington state. It will add another 200 stations in the metropolitan New York area and recently announced similar agreements for debit-card service in Pennsylvania and upstate New York.

Mobil said that after expanding in the Northeast, it will extend the service to the Midwest.

In all, Mobil plans on having 3,600 electronic sales systems in 25 states by next fall. Not all of those systems will offer debit-card purchases.