One of the myths about affluent Washington consumers is that their pocketbooks and wallets are stuffed with plastic -- dozens of credit cards flashed at shopping malls around the Beltway for the purchase of as many goods and services as possible.

The Sindlinger research organization, several years ago, called Washington's suburbs the land of milk and honey, supposedly populated by persons who cared little about the economic weaknesses elsewhere in the country or even in the relatively poorer sections of the capital city itself.

A new public opinion sampling, however, indicates that many Washingtonians are about as cautions in the use of credit cards as average Americans.

The poll, conducted for The Washington Post by the Southeastern Institute of Research Inc. in Richmond found that the average number of credit cards among the metropolitan area population is 4.1. For households with at least one credit card, the average of cards held is five.

Generally, cardholders here seem to be using their cards less in the wake of new government credit controls. They either are paying the same amount or paying more on their monthly payments.

Moreover, fully 17.6 percent of area consumers have no credit cards at all. Where the head of household is among the key 35-to-44-year-old buying sector of the metropolitan population, 23.7 percent of the households have no credit cards and among residents 65 years or older, 28.1 percent have no credit cards.

Nationwide, according to the National Federation for Consumer Credit, the average number of cards held by a credit-using family is 4.2 cards. In the Washington area, 57 percent of the families either have no cards or have fewer cards than the national average, according to the new survey.

At the other end of the spectrum, 14 percent of the area households do have 10 or more cards, with the highest concentration being in homes where the household head is at least 45 years old and under age 65.

The Southeastern Institute conducts monthly public opinion samples in the Washington area, contacting 300 male or female household heads by random telephone calls. The latest poll was conducted between March 20 and March 27, after federal credit controls were announced.

Among the key findings:

More credit cards are held by households where the head is a college graduate.

In terms of family income, 38.5 percent of households with annual incomes uner $10,000 have no cards while only 6.6 percent over $30,000 have no cards.

Households headed by clerical, sales, professional and managerial workers have more credit cards than service workers, craftspeople, military and retired persons. Indeed, as befits percise military operations, exactly 14.3 percent of military homes have one card; 14.3 percent, two; 14.3 percent, three; 14.3 percent four; 14.3 percent, Five; 14.3 percent, six and 14.3 percent 10 or more.