40 percent of the market -- and will influence 80 percent of all new-car sales.

Conde' Nast Publications, figuring that women likely to buy new cars also are the types who read its magazines, recently completed part two of a study, "The Women's Market for New Cars." Part one, completed late in 1981, identified specific differences in men's and women's attitudes toward automobiles and gave advertisers an idea how to hit the "much larger, mostly untapped and unadvertised-to women's market."

Part two is a detailed view of American women and their car-buying habits. Among the latest findings:

* Seventy-two percent of the women surveyed purchased American-made cars within two years of the latest study; 23 percent bought Japanese-made cars; 5 percent bought European-made cars.

* Looking forward, 79 percent of the domestic-car buyers said they would buy American again, while only 39 percent of those who bought Japanese cars said they probably would purchase Japanese cars again. European-car buyers "reported similar intentions for future purchases."

* Women buying American-made cars made up the oldest group, with a median age of 43.1, and 46 percent 45 or older. Women buying Japanese cars were the youngest group, with a median age of 34.9.

* European-car buyers were the most affluent and best-educated group but they only made up 5 percent of the overall female market. They had a median income of $40,560 and two-thirds were college graduates. Check It Out

If you're thinking about buying a used car, consider running its model and year data by the National Highway Traffic Safety Administration. The agency can tell you whether that make, model and year car has ever been recalled, how to find out whether the defect was taken care of and what to do if it hasn't. 800-424-9393. In the District: (202) 426-0123. Flags Up

As a distress signal, stranded motorists often tie a handkerchief to the radio antenna or driver's-side door handle. Now a Pennsylvania company has come up with three color-coded flags for car owners to indicate the kind of help that's needed.

The firm, Universal Distress Systems, produces 18-inch flags that can be hung out the driver's window: fluorescent red, with a cross and the word "medical," to indicate a medical emergency; blue, with the word "service" and a gas-pump symbol; and yellow, with "mechanical" and a wrench and screwdriver.

The kits ($9.95) are available from Contacts Unlimited, 6881 Brian Michael Court, Springfield, Va. 22153. For information on group or large-quantity discounts, call Robbie Motter, (703) 644-1713.