43% of American college students using credit cards

College students may not have much excess folding money stuffed in their jeans' pockets. But they do have ''plastic money.'' According to a recent survey by Simmons Market Research Bureau, the almost 4. 5 million full-time undergrads continue to represent a sizable consumer market - maybe as much as $1 billion a year. And a sizable part of their buying is being done on credit: Forty-three percent use their own personal credit cards.

So what are they buying?

Checking a year's worth of purchases showed that 21 percent bought four pairs of jeans; 41 percent, sweaters; and 21 percent, exercise sweats. Forty percent were regular users of oral hygiene and personal care products. As for athletics, over half said they were dedicated joggers (buyers of shoes, socks, shorts, accessories, and exercise equipment); some 60 percent own a bicycle.

The credit card most mentioned by respondents was Visa (12 percent), with Sears, Roebuck & Co. a close second (11 percent). Retailing officials say this latter prominence could be due to Sears' early recognition of the student buying trend.