Defense consultant William Parkin, hospitalized 10 days earlier for an apparent suicide attempt, pleaded guilty to charges he schemed to bribe a Navy engineer who helped Parkin's industry clients on contract awards.

Parkin, 65, who received a medal in 1983 when he retired as a senior Pentagon procurement official, hung his head and spoke softly Monday while entering his pleas to three counts: conspiracy, bribery of a public official and wire fraud.A divorced father of four, he faces a maximum sentence of 25 years in prison and fines of up to $750,000.

Parkin is regarded as a key figure in the FBI and Naval Investigative Service's sweeping "Operation Ill Wind" probe of allegations industry consultants bribed defense procurement officials for contract information.

Investigators have evidence - including wiretapped telephone conversations - that a dozen or more consultants ran a ring of corruption that involved scores of government and industry figures and tainted the awarding of defense contracts worth hundreds of millions, if not billions, of dollars, federal law enforcement sources say.

Parkin's plea was described by a federal law enforcement source as "significant" because of his pledge to cooperate fully with investigators.

Parkin told U.S. District Judge Claude Hilton he was satisfied with the terms of his plea agreement. His lawyer, Gerard Treanor, told reporters Parkin's "health is improving."

Law enforcement sources said Monday they expect Parkin to provide information that touches on other aspects of the inquiry. For example, Parkin has been a friend of high-powered consultant William Galvin, a partner of former Assistant Navy Secretary Melvyn Paisley. Galvin and Paisley both are targets of the investigation.

The scheme involving Parkin, the focus of the first indictment in a nearly 3-year-old investigation, has now led to guilty pleas by five individuals and his two contractor clients, the Hazeltine Corp., a subsidiary of the Emerson Electric Co., St. Louis, and Teledyne Industries Inc., Newbury Park, Calif.