Mention the word "credit" and most college students worry about having enough to graduate. Yet, with around 84 percent of Harvard students carrying credit cards, perhaps they should reach for their wallets instead of their course guides.

The large number of college credit cardholders is indicative of aggressive marketing by companies such as American Express, MasterCard and Visa. Not only do many of these companies waive minimum income requirements, they also offer incentives aimed at college students.

By broadening the scope of their marketing, they have won over many college students who will likely become loyal customers.

The business of buying on credit first captured the national limelight in 1938 when oil companies' customers created accounts to simplify transactions.

And since the creation of the first credit card--the Diners' Club Inc. in 1950--it has exploded into a multi-billion dollar industry that will involve approximately 87.5 million American cardholders by the year 2000, according to Statistical Abstract of the U.S.

But the credit card craze is not limited to credit card companies like American Express, MasterCard and Visa. Retail, oil and phone companies have created their line of credit cards for customers.

In 1989 according to the Nilson Report, 82.1 million people owned credit cards from oil companies, 103.6 million held accounts with phone companies and 95.4 million carried credit cards from retail stores.

And the market for new credit cardholders is engulfing more and more college students each day.

American Express, founded in 1958, has aggressively pursued the college market since the 1979 creation of its student marketing department. It is the credit card company that offers the most incentives intended to woo college students into the world of credit.

In addition to waiving the usual minimum income requirements of $25,000, American Express accepts unusual sources of income when granting accounts to students. Because students do not ordinarily work during the academic year, the company accepts funds such as scholarships, loans, work-study and allowances from parents as verifiable sources of income, says Director of Student Marketing Diane Ty.

Other benefits include four round-trip tickets on Continental Airlines costing less than $100 each way and free subscriptions to the money management magazine Connections geared specifically towards college students.

American Express also offers up to 30 minutes each month of free long-distance calling from MCI and special discounts to various merchants and retailers.

Just recently, the credit company signed a deal with J. Crew in which college card holders can get a discount of up to $20 on purchases of $100 or more.

Although American Express would not disclose what percentage of their business centers on college students, Ty says they approach the college market with the aim to recruit long-term customers.

"Students often go on to become some of our best and most loyal customers," Ty says.