Three members of the "Legion of Doom," a group of computer hackers, pleaded guilty yesterday to charges involving a scheme to steal computer access codes from BellSouth Corp., the Justice Department and the company said.

Joe D. Whitley, U.S. attorney for the Northern District of Georgia, and Dwight D. Ellison, special agent in charge of the Secret Service's Atlanta field office, said yesterday that three Atlanta men -- Adam E. Grant, Franklin Darden Jr. and Robert J. Riggs -- conspired between Sept. 10, 1987, and July 21, 1989, to commit computer fraud, wire fraud and access code fraud and to transport stolen property across state lines.

Scott Ticer, spokesman for BellSouth, said that incidents in which the men were involved cost the firm $1.5 million. The bulk of the expense, he said, was management time spent investigating the case and also to change the passwords of the firm's computer system. Ticer said that BellSouth has had several intrusions into its systems, as have "most businesses with any computer system."

Dale Boll, assistant special agent in the Secret Service's fraud division, said that the firm is estimated to have lost $372,000 in software and services, while credit card losses amounted to $800,000.

Darden and Riggs pleaded guilty to one conspiracy count each. Both face a maximum penalty of five years in prison and a $200,000 fine. Grant pleaded guilty to possessing 15 or more BellSouth access devices with the intent to defraud. He faces a maximum penalty of 10 years in prison and a $250,000 fine.

According to the government's evidence, defendants called various BellSouth computer systems without authority and obtained computer access codes, which they distributed to other computer hackers. Boll also said that the three were able to manipulate BellSouth's system so that calls made by regular phone users to Daytona Beach would be diverted to the city's information number.

The Justice Department said that if the case had gone to trial, the government was prepared to prove that the defendants and others had the ability to compromise telephone service in the four-state BellSouth area and throughout the country.

The Secret Service investigates cases of suspected computer fraud under federal laws designed to protect the increasingly widespread role of the computer in the United States.

A particularly prominent group of hackers, known as the Legion of Doom after cartoon characters, has drawn special attention.

According to yesterday's announcement, the Legion has some 15 members operating in Georgia, Texas, Michigan, Illinois, Florida, New York and other states.