ATLANTA (AP) _ An Atlanta woman who says her stockbroker used her investment account to generate more than $1 million in commissions for himself has been awarded $3.1 million by an arbitration panel.

In one of the biggest securities case awards ever, the National Association of Securities Dealers disclosed Tuesday that an arbitration panel ordered that Nancy L. Cooper, 42, be paid $1 million by broker D. Elliott Dahle Jr. and $2.1 million by Shearson Lehman Hutton Inc., his former employer.

Dahle declined comment on the award. Mrs. Cooper also declined comment.

Shearson Lehman spokesman Steven Faigen in New York said the brokerage would appeal the decision.

Mrs. Cooper charged that Dahle traded in her account to generate commissions - a process called ''churning'' - and breached his fiduciary duty, purchased stock on credit without her permission and bought investment products that were unsuitable.

NASD also ordered Dahle and Shearson jointly to pay attorneys' fees and other expenses involved in the litigation, which lasted more than seven months.

Mrs. Cooper's attorney, Marion Smith II, said the woman's actual monetary loss totaled about $200,000 on stocks and an undetermined amount on the limited partnerships.

In addition, lost investment opportunities cost Mrs. Cooper more than $2 million, according to NASD arbitration documents filed Tuesday in federal court.

Mrs. Cooper's father was one of the founders of Oxford Industries and Lanier Business Products, two Atlanta-based companies.

Over a period of several years, Dahle became such a trusted adviser of Mrs. Cooper's that she approved whatever he recommended, even though she was not sophisticated about investments, according to the NASD complaint.

Smith said that about half of all the stocks Dahle purchased for Mrs. Cooper were sold in less than 30 days.

Mrs. Cooper's complaint charged that Dahle generated $132,972 in commissions in 1985, $852,202 in 1986 and $17,272 in 1987 by trading in her account.