PERHAPS AT THIS point in the season there is more green in living rooms than in wallets, but anyone who still can and does deal in cash once in a while may be pleased to discover that this old-fashioned form of transaction is making a bit of a comeback: not only are more stores offering various discounts or incentives for cash, but the idea also has been spreading to gasoline stations around town. First came the gas-and-go, no-service places that insisted on cash as part of their lower-pricing deal with drivers; and now, because one major oil company is charging its dealers a fee for every credit card transaction, even some of the traditional "service" stations are making adjustments to serve cash customers at lower rates.

Sparking the change for many stations is a decision by Texaco, Inc., to require its dealers to pay a 3 percent surcharge, or processing fee, on all credit-card invoices submitted to the company. Though this may be correctly read as another exchange in the less-than- great relationships between big oil companies and their dealers, it is being misunderstood by customers who prefer to use their credit cards; they are complaining about stations that differentiate between cash and credit prices at their pumps.

For example, at the Van Ness Texacare Servicenter on Connecticut Avenue NW you will find three different prices for the same type of gasoline: a gallon of regular gasoline has been going for $1.26 at a self-service, cash-only pump; for $1.33 self-served and by credit card; and $1.59 at the full-service island. Yet other Texaco dealers have said this system has drawn strong opposition from customers-- leaving them two other choices: either they absorb the company's surcharge or they spread it among all customers, cash-carrying or not.

Certainly there are costs attached to the paper work of credit transactions, and in other retail businesses, the cash customer--like it or not--usually winds up helping to cover those costs that are charged to dealers by, say, American Express, for each sale on its card. Thus, if there is still anything to the assumption that you get what you pay for, you should pay the most for credit and old-fashioned filling-station service; less for pumping your own gas and charging the sale; and even less for pumping and paying on the spot.

As for how many more companies will start charging their dealers for credit processing--or how they may alter dealer contracts to do so-- that is a separate question, posed in a pending federal court suit. Two Philadelphia dealers, on behalf of all Texaco dealers, are charging that Texaco has illegally and unilaterally modified dealers' contracts and violated antitrust laws by trying to restrain trade and business of Texaco dealers. Final arguments are scheduled for Jan. 5.

But while other companies await the outcome of this case before deciding how or if they will impose extra charges for credit, customers who don't wish to pay for credit should get some for putting their money where their sales are.