Two key figures in a federal investigation of Maryland state construction contracts worth millions of dollars have secretly pleaded guilty to felony offenses, agreeing to go undercover to help in an investigation involving an influential former state senator.

Although the charges against builder Michael C. Forti and his wife, Geraldine E. Forti, were made public Tuesday, their guilty pleas were not disclosed until yesterday. Their agreements to cooperate with prosecutors date to July, according to documents unsealed at U.S. District Court in Baltimore.

The guilty pleas suggest that the pace of a long-running probe involving Thomas L. Bromwell has quickened dramatically. For two years, the investigation has been the subject of wide speculation in Annapolis, where the Baltimore County Democrat was a powerful figure in the state legislature before resigning in 2002 to lead a state agency.

The documents unsealed yesterday say Poole and Kent, a large commercial builder that won lucrative state jobs when Bromwell was chairman of the Senate Finance Committee, used a front company to appear to satisfy requirements for the participation of minority- and women-owned firms in construction projects. The arrangement is described in a factual summary prepared by prosecutors accompanying the plea agreement of Michael Forti, a former executive vice president at Poole and Kent.

Beginning in 1999, Poole and Kent used Namco Services Corp., a contracting firm owned by Geraldine Forti, as a "minority front," the statement says. In exchange, Geraldine Forti received regular payments disguised as paychecks from Namco, the statement says.

Poole and Kent hired Namco as a subcontractor to appear to meet minority requirements on more than a dozen projects, including the expansion of a terminal at Baltimore-Washington International Airport and the construction of a juvenile justice center in Baltimore, it says. Namco's subcontracts totaled $4.87 million.

The statement says the arrangement was proposed by W. David Stoffregen, a former president of Poole and Kent. A message left late yesterday at Stoffregen's home was not returned, and there was no answer at the offices of Poole and Kent.

Michael and Geraldine Forti pleaded guilty during a proceeding that was closed to the public, and the clerk's file did not include their pleas until yesterday. The justification for the unusual secrecy was unclear yesterday. The judge, J. Frederick Motz, did not return a phone call, and a spokeswoman for U.S. Attorney Rod J. Rosenstein said she could not comment. Calls to the defendants' lawyers were not returned.

Michael Forti pleaded guilty to mail fraud and filing a false tax return. Geraldine Forti, whose company once employed Bromwell's wife, Mary Pat, pleaded guilty to filing a false tax return. They pleaded guilty in exchange for leniency and for immunity from criminal charges involving any further disclosures they make while cooperating with investigators.

The couple also admitted they filed tax returns for three years that did not reflect more than $635,000 worth of work done by Poole and Kent and its subsidiaries on a home they built in Middle River. Under the agreement, they pleaded guilty only to falsely reporting their 2000 income.

The court documents do not mention Bromwell. His attorney, Robert Schulman, declined to comment yesterday.

A handful of Bromwell's former staff members and Senate colleagues have appeared before a grand jury examining the senator's ties with Poole and Kent. Questions have focused on state contracts given to the contractor during the years when Bromwell was in the Senate, including the construction of the $41 million juvenile justice center in Baltimore, a contract for which the company was not the lowest bidder.

The one-time tavern owner rose through the ranks to become chairman of the Senate Finance Committee. He left the Senate to head the state's Injured Workers Insurance Fund, where he received a pay package worth more than $250,000 a year.

Ex-state senator Thomas Bromwell is the subject of a grand jury probe.