BALTIMORE, JULY 31 -- Investigators have begun a widespread probe of alleged construction bribery and fraud at the U.S. Naval Academy in Annapolis, federal prosecutors said today.

One Annapolis plumbing and air conditioning contractor pleaded guilty in federal court here today to giving illegal gratuities, acknowledging that he gave more than $20,000 in cash and household appliances to the academy's former public works chief in exchange for preferential treatment.

More charges are expected, investigators said.

The contractor, Carroll R. Dunton, 65, also pleaded guilty in a separate case to bribing former Annapolis Housing Authority chief Arthur G. Strissel Jr., who was convicted in 1988 of accepting thousands of dollars in cash, home renovations and other gifts from four contractors, including Dunton.

In the Navy case, academy officials had little to say, except that they are cooperating with investigators from the FBI and the Naval Investigative Service.

The academy is already being investigated by several military and congressional panels looking into allegations ranging from improper hazing of midshipmen and harassment of women to the theft of exams and other abuses of the honor system.

The contract probe, which began with an anonymous tip to a Department of Defense whistleblower hot line in March 1989, has spread beyond the Dunton case to "all work being done by the {academy's} public works office," according to Breckinridge L. Willcox, U.S. attorney for Maryland.

The public works office approves all construction and repairs on the academy's 338-acre campus and has final responsibility for all contract awards. The office was commanded by Capt. James Edward Weston from 1985 until shortly before his retirement last October.

According to a statement filed in court today by prosecutors Jane F. Barrett and Roann Nichols, Dunton plied Weston with at least $20,307 in cash and assorted household appliances "in hopes that Weston would use his influence, if necesssary, to benefit Dunton's company," Dunton Inc.

At various times, the statement said, Dunton gave Weston a washer and dryer, several air conditioners, a dishwasher, a trash compactor, five water purifying systems and a lawn mower, all for Weston's home on the academy grounds. Dunton also paid $535 for the rental of a Lincoln Continental used by Weston.

In addition, Dunton paid for $12,780 in Amway products from Weston's wife, Mary, the statement said, but he never received the products or a refund.

During this time, according to the statement, Dunton received numerous contracts, including several that were priced well above government estimates.

Shortly after Dunton provided the washer and dryer in 1985, for example, Weston recommended Dunton as a "preferred bidder" on Navy work. Dunton then won a $2.8 million contract for work on the Navy's Communication Research Facility at nearby Chesapeake Beach, the statement said.

After Dunton furnished several air conditioners in 1986, he won a $961,333 contract to install heating, ventilation and air conditioning in the academy's Rickover Hall, a large classroom building, even though his bid was 55 percent over the government estimate of $619,236, according to the statement.

In September 1989, the Naval Audit Service, assisting in the investigation, reported that Dunton's company received about 25 percent of all construction contracts awarded at the academy during Weston's tenure as public works officer.

"Many of these contracts were awarded despite the fact that Dunton's winning bid was more than 15 percent over the government estimate," the statement said.

The public works annual budget could not be learned today.

Eugene Hook, a civilian employee in the public works office, who had access to government estimates and other key data, frequently dealt with Dunton and sometimes relayed messages to him about air conditioners and other appliances that Weston wanted provided for his home, according to the statement.

Weston, reached by telephone last night at his home in Nevada and told of the prosecutors' statements, said, "I really don't have any comment. That really just baffles me."

Weston and Hook, along with others at the academy, are subjects of the investigation, officials said.

Dunton has been scheduled for sentencing Oct. 26 by U.S. District Judge John R. Hargrove on both the academy charge and the Annapolis housing charge. He faces a possible maximum of 12 years in prison and $500,000 in fines.

He remains free on personal bond pending sentencing.