Federal prison inmates soon will be required to attend classes until they can read at the 12th-grade level and complete a high school equivalency degree, the Justice Department said yesterday.

If they refuse to do so, they will be consigned to the lowest-paying prison jobs and could be subject to disciplinary actions, the department said.

Federal prisoners are already required to attend classes if they cannot read or perform mathematics problems at the eighth-grade level.

Under the higher standards, effective early next year, inmates will be required to master 12th-grade academic skills by attending prison classes, the department said.

There are other incentives for completing the program: an inmate eligible for parole would not want any comments about disciplinary actions to be seen by the parole board, said Gregory L. Bogdan, a Bureau of Prisons spokesman.

Tougher literacy standards are intended to raise the chance that inmates will not return to crime once they are released from prison.

"For most who cannot read, competing in the legitimate work world is impossible," Attorney General Dick Thornburgh said in remarks prepared for delivery to an international conference on prison literacy in Ottawa.

"We live in a complex world, and the pressure of competition for good-paying jobs, and indeed success in virtually every aspect of modern life, hinges on literacy," Thornburgh said.

The higher standards are being imposed at a time when 20 percent of the 58,000 federal inmates cannot read at the eighth-grade level and 40 percent have a history of drug or alcohol abuse.

Last year, 10,546 federal inmates completed eighth-grade requirements and 3,100 finished high school equivalency programs, Thornburgh said.

The Education Department says up to 30 million U.S. adults are illiterate.