A Metro task force has asked the system to study the possibility of allowing Metrorail riders to purchase Farecards with major credit cards.

The credit cards system, as described by the task force, would allow commuters to use their major credit cards -- for example, Visa, Mastercharge, American Express -- to purchase Metrorail rides in Quantities from specially designed vending equipment at each station.

The cards would be inserted into an electronic "slot reader" at subway station entrance and exit gates. The reader would scan a magnetic tape on the back of the card and open the gate. Each transaction would be recorded in a central computer, which would send daily billings to credit card companies.

"A program could be devised to honor all credit cards," the task force said in its report. But for administrative convenience it might be better to require a special Metro credit card."

"We don't know how much such a system would cost," said Robert Pickett, a task force member and a transportation planner at Metro. "But we believe it is a good idea for Metro to be looking at with a great deal of seriousness."

Cubic Western Data, the San Diego based corporation that installed Metro's $55 million Farecard vending system, also manufactures the type of reader that could be used for credit card billings.

Similar machines made by Cubic Western, are already in use to sell airline tickets at 45 airports around the country, including National Airport here.

"The same equipment we are using at the airports could be adapted to sell Metro farcards," said Tom Tuttle, Cubic's director of marketing. "We think that one problem is you might end up at the end of the month with a half dozen $80 sales and the rest essentially small purchases," Tuttle said. "We're not sure that banks would be happy with that because of the amount of costly computer time it would take to keep track of the transactions."