The U.S. government's largest dredging services contractor and a subsidiary have agreed to plead guilty to charges of nationwide bid rigging schemes and pay the government $8.26 million in criminal fines and civil antitrust settlements, according to federal law enforcement agencies.

The pact came after a two-year investigation into allegations of antitrust violations by dredging contractors hired by the Army Corps of Engineers for projects throughout the nation, the Pentagon's inspector general and the Justice Department said.

The Justice Department has filed four criminal "informations," equivalent to grand jury indictments, against Great Lakes Dredge & Dock Co. of Oak Brook, Ill., for conspiring to rig bids on four projects.

Great Lakes and one of its subsidiaries, North American Trailing Co., have agreed to pay criminal fines totaling $4.26 million for the four projects as part of a plea bargain in which the Justice Department agreed not to bring any further charges against the companies for conspiracies to rig bids on dredging projects. Great Lakes also has agreed to pay the government a $4 million civil settlement.

A spokesman for Itel Container Corp. of San Francisco, which has acquired Great Lakes, said the company has now set up self-policing programs. The parent firm acquired Great Lakes after the bid rigging had been conducted. Five former executives and employees of Great Lakes, including its former president, have faced criminal penalties and fines after being convicted or pleading guilty in connection with the cases, according to spokesman Gary Hill.

The four alleged bid rigging schemes cited by Justice and investigated by the Defense Criminal Investigative Service include:

A Philadelphia case in which Great Lakes is accused of conspiring with others to rig bids in May 1985 on a $5 million hydraulic dredging project on the Delaware River.

A New Orleans case in which the firm is accused of bid rigging on a dredging project in the Gulf of Mexico from April 1983 to June 1984.

A Cleveland case charging that Great Lakes conspired to rig the bids on a $2.6 million clamshell dredging project.

A San Francisco case alleging the company conspired to rig bids on a $3.6 million dredging project.