The computerized letter from Amoco Oil Co. was brief and to the point: Claire Cherry of Atlanta had been rejected for a credit card because of income level, type of bank references and the company's credit experience "in your geographical area."

It wasn't the Deep South, or Georgia, or even Atlanta that Amoco disapproved of; it was Cherry's neighborhood, as disclosed by her postal zip code. She is a white divorcee who makes about $14,000 a year, which should be ample to pay her gas bills. But she lives in a zip that has been zapped by Amoco's credit analysts as a neighborhood of poor credit risks. So, no credit card.

The geographic gimmick Amoco uses in its "credit scoring system" is the subject of an investigation by the Federal Trade Commission. The FTC's concern is that the use of zip codes, particularly in urban areas that are still largely segregated, is just a sneaky way of discriminating against minorities.

Amoco insists that an applicant's location alone is never the main reason for refusing a credit card. The zip code is only one of 14 criteria on which applications are judged. On the other hand, Amoco told our associate Tony Capaccio that their system works that zip codes can indeed be used to predict high credit risks.

Few creditors use the zip code in their scoring system, and Amoco is apparently the only major oil company that does. Under the Amoco system, the nation's 39,462 zip codes are classified on a scale of 1 through 5; applicants in Class 4 or 5 have the best chance of approval, those in Class 1 or 2, the worst.

Amoco puts only 855 zip code areas in Class 1 or 2 in the country, but the effect can be significant on a credit card applicant's rating. In most states where Amoco does business, a minimum score of 55 points is needed for approval. An applicant who lives in a Class 1 zip area is automatically penalized 17 points, no matter what his or her credit history may be; for a Class 2 nieghborbood, the penalty is eight points.

Investigators have found a nationwide pattern in the zip code users. As a general rule, the greater the percentage of minorities in a zip code area, the greater the likelihood that it will get a low classification.

In Atlanta, for example, a Georgia State University sociologist analyzed city zip codes that Amoco had relegated to Class 1 or 2. He found that 73 percent of Atlanta's nonwhite population was concentrated in these zones and only 23 percent of the city's whites.

"It was found that as the percentage of nonwhites in each zip code was increased, the percentage of credit applications approved decreased," the analysis showed. "That above data indicates that the denial of credit is strongly and significantly related to the nonwhite racial composition" of the zip code zones.

In Massachusetts, state attorney general's investigators found a similar pattern in the zip code neighborhoods that Amoco had in effect blacklisted. The findings particularly incensed Sen. Paul Tsongas (D-Mass.) who feels the Amoco system of "neighborhood slight" strongly discourages restoration of rundown urban areas.

The FTC is quietly working on a consent agreement for Amoco's consideration; the company would agree to stop using zip codes in its credit scoring system, without admitting any wrongdoing in the past. Massachusetts has filed suit against the oil company, charging that blacks are twice as likely as whites to be rejected for credit cards under the Amoco system.

For its part, Amoco claims that if it is forced to abandon the use of zip codes, it would have to turn down about 28,000 more credit applications a year than it does now.

Washington Whirl -- Among those who were not invited to Camp David to give Jimmy Carter advice was a little known expert who could have given the president an earful on a long-ignored way to help the country out of its energy crisis. He is Dr. Paul Bente a softspoken chemist who spent 27 years with Dupont and now heads the Bio-Energy Council, a nonprofit organization that keeps track of research in the conversion of organic material into fuel that can heat homes, power generators and run automobiles.

This "biomass energy" already provides 2.5 percent of the nation's energy. But Bente believes that with a concerted effort this amount could be increased five to 10 times in a few years -- and without polluting the land or atmosphere. It's not too late to consult Dr. Bente. His office is at 1625 ISt. N.W., Washington, D.C. 20006 -- two blocks from the White House.