Marathon Oil Co. has agreed to plead guilty to criminal charges and pay a $900,000 fine for pollution, the government said.

U.S. Attorney Deborah J. Daniels said Marathon also agreed to spend $3 million during the next two years to correct problems at its northwest side Indianapolis refinery that it acquired March 9, 1989, from the Rock Island Refining Corp.The charges against Marathon, based in Findlay, Ohio, and with operations also in Houston, deal with the discharge of pollutants during May 1989.

Daniels said the investigation of the refinery began following an explosion and fire at a home about two miles southeast of the refinery and located on the sewer line leading from the refinery.

Shortly after the explosion on May 26, 1989, Daniels said, measurements taken in the sewer system at the refinery's discharge point showed 100 percent levels for explosivity. Any level over 10 percent is considered unacceptable, according to an Indianapolis ordinance.

Daniels said Marathon agreed to plead guilty to one felony count of knowingly bypassing a portion of its waste water treatment facility, one misdemeanor count of negligently failing to report the bypass to authorities and one misdemeanor count of negligently introducing a pollutant into the city sewer system that could create a fire or hazardous explosion.

All counts cite violations of the U.S. Clean Water Act.