A former purchasing specialist for the U.S. Postal Service pleaded guilty yesterday to accepting nearly $800,000 in bribes from businesses that received preferential treatment on printing contracts.

Daniel J. Williams Jr., 62, of Accokeek took the payments over 12 years and used the money to buy a Prince George's County home and such luxuries as a Corvette and a diamond-studded Rolex watch, prosecutors said.

"This case demonstrates how one corrupt public official can have a malignant effect on the integrity of our public contracting system and the private businesses that provide services to the government," U.S. Attorney Kenneth L. Wainstein said after Williams pleaded guilty in U.S. District Court in Washington.

Federal authorities conducted a year-long investigation into Williams's dealings with eight companies after receiving an anonymous tip through a Postal Service hotline, according to charging documents. Owners of four companies have pleaded guilty to charges that they paid Williams to obtain contracts. The other four are under investigation.

Under federal sentencing guidelines, Williams faces up to 78 months in prison on charges of receiving bribes and conspiracy to commit money laundering. His sentencing is set for early next year.

Williams admitted taking bribes from the printing companies and, in turn, providing them with confidential bid information and contract awards, according to charging documents. Prosecutors said Williams punished companies that refused to pay him.

At least one company owner who pleaded guilty in the case aided investigators by secretly tape-recording conversations with Williams, prosecutors said. The probe was conducted by the Postal Inspection Service, the Postal Service's inspector general and the FBI.

Williams, a 32-year employee of the Postal Service, worked at its headquarters at L'Enfant Plaza until his retirement in September 2003. He was accused of concocting an elaborate scheme to thwart authorities that included depositing bribe money into several bank accounts so it could not be traced to him.

Most of the payments were made in cash, prosecutors said. But others were given in a more roundabout way. One vendor paid attorney's fees stemming from Williams's divorce from his first wife, prosecutors said. Another purchased the invitations for Williams's wedding to his second wife, they said.

Vendors also regularly gave Williams tickets to Washington Redskins and Wizards games and Baltimore Orioles games.

Reached at his home yesterday afternoon, Williams declined to comment. His attorney, Monte D. Montgomery Jr., did not respond to several requests for comment.

As part of the plea agreement, authorities will confiscate Williams's house, Corvette and Rolex.