ATLANTA — Lawyers pressing a racial discrimination lawsuit against U.S. electricity giant Southern Co. and several of its subsidiaries said Monday they had added four black workers to the lawsuit and would press for class-action status to cover more than 2,000 others.

The lawsuit, filed last month in Atlanta's Fulton County Superior Court by three workers, accused Southern Co., its Georgia Power unit and one other subsidiary of discriminating against blacks in pay and promotions and subjecting them to harassment in the workplace.

The amended suit named an additional Southern Co. subsidiary as a defendant. Southern Co., the nation's largest electricity producer, denied that it tolerated discrimination within its ranks.

"The fact that discrimination exists in more than one of Southern Co's subsidiaries is not a coincidence but rather a direct reflection on Southern Co's common and far-reaching employment policies and practices that allow managers' racially-biased employment decisions to stand unchecked,'' said Steven Rosenwasser, an attorney for the law firm Bondurant Mixson & Elmore, which represents the plaintiffs.

The lawsuit alleged the companies, particularly Georgia Power, had maintained a glass ceiling that virtually excluded blacks from obtaining positions of power, resulting in a severe under-representation at senior levels.

The companies were also accused of failing to take action when alerted to racially offensive acts, including the alleged display of two hangman's nooses on company property and the use of the word "nigger'' to refer to black employees.

Blacks, especially in the Deep South, view hangman's nooses as a potent reminder of a time not so long ago when angry white mobs regularly lynched blacks.

Southern Co. said the changes to the lawsuit would not alter the company's determination to thoroughly investigate the allegations of racial discrimination, which it described as ''very serious.''

"Southern Co. (including its subsidiaries) maintains a strong policy of zero tolerance for discriminatory or racially intolerant behavior,'' said Southern Co. spokesman Todd Terrell, who noted the issue was a top priority for management.

Southern Co. is the latest in a growing list of companies based in the U.S. South that have been slapped with racial discrimination suits.

Atlanta-based Coca-Cola Co. , the world's largest soft drinks company, recently reached a tentative settlement of a racial bias suit filed by a group of former and current black workers. The beverage giant currently faces another such suit.

Home improvement retailer Home Depot Inc. , also headquartered in Atlanta, has been sued for alleged racial discrimination against black workers and at least one black customer.

Southern Co. shares rose 1/8 to 27-5/16 Monday on the New York Stock Exchange.