CHICAGO (AP) _ One of the state's best-connected lobbying firms has pleaded guilty to mail fraud and agreed to pay a $350,000 fine in connection with bid-rigging in the $800 million expansion of Chicago's McCormick Place convention center.

Ronan Potts LLC also agreed Thursday to forfeit $67,000 in payments it received from a St. Louis-based company to help land the $11.5 million contract to oversee the expansion.

Neither of the top managers of the lobbying company, Al Ronan and John Potts, have been accused of wrongdoing in the case. Ronan, a former legislator, has been a major fund-raiser for former Gov. George Ryan and other Illinois politicians.

The firm ranks among the most successful in the state, with a client list that includes local governments, liquor distributors and gambling companies.

The plea was entered by attorney James Cutrone on the firm's behalf.

After the hearing, Cutrone said the firm is eager to pay its fine and ``get on with business.''

``They've lost a few clients _ not many,'' he said.

Under an agreement with federal prosecutors, the firm can withdraw its guilty plea if U.S. District Judge Blanche M. Manning fines it more than the proposed $350,000. Under the law, she could go as high as $700,000.

The firm would be on probation for two years under the agreement.

Four others who prosecutors say were involved in the bid-rigging, including former Ronan Potts vice president Julie Starsiak, also have pleaded guilty. Former Ryan chief of staff and campaign manager Scott Fawell has pleaded innocent and is due to go on trial Sept. 20.

Fawell is serving 6 1/2 years in federal prison for a racketeering conviction involving the use of taxpayer dollars and state employees to fuel Ryan's election campaigns for almost a decade.

The charges are part of a broader federal investigation that has led to indictments against dozens of state employees and others, including Ryan, who has pleaded innocent to racketeering charges.

Prosecutors say that at Fawell's direction, his assistant told Starsiak the amounts contained in the sealed bids on the contract to oversee the expansion. Starsiak admits giving the information to a client, Jacobs Facilities Inc., which won the contract after cutting its bid from $18.8 million to $11.5 million.