Four years ago, Philip R. Brooks took charge of Virginia's central purchasing agency with a mandate from then-Gov. Mills E. Godwin to straighten out some of its management problems.

Today. Brooks says his Department of Purchases and Supply, which buys $80 million annually in food, furniture, printing and other supplies and services, "has done a tremendous job," and has saved the state significant sums of money by efficient purchasing practices.

Nevertheless, he finds himself enmeshed in allegations of favoritism to a few printing companies and one furniture manufacturer - allegations that have resulted in investigations by the state police, and, it was announced Thursday, the FBI.

Brooks himself asked for the state police probes. One terminated in the resignation of a senior purchasing official. The other is still under way. It apparently is focusing on furniture purchases, but Brooks declined in an interview to discuss it. The FBI is taking part in that investigation.

A spokesman for Gov. John N. Dalton said yesterday that the governor "is anxious to get to the bottom" of allegations of purchasing favoritism, but has so far played no personal role in the investigation.

The agency that Brooks took over after a career in private industry handles purchases for every state agency except the mammoth Department of Highways and Transportation and Virginia's three largest universities.

Despite apparent similarities in the pattern of alleged favoritism, Brooks is quick to reject any comparison of the Virginia department with the scandal-ridden General Services Administration, the purchasing and real estate agent for the federal government.

Unlike the federal agency, he said, the Virginia department does not write specifications for supplies and equipment bought by state agencies.

"The requisitioning agency writes the specs," he said, "we just do the purchasing."

It is this circumstance that apparently has led to charges of favoritism to InterRoyal Corp., a New York manufacturer that dominates furniture sales to Virginia mental hospitals and some other institutions.

"Back in 1975, it was called to my attention by my purchasing agent, Roy Scott, that furniture specs were being written so tightly that only InterRoyal could qualify for some contracts," Brooks said. "We had a meeting with the Department of Mental Health and Mental Retardation officials to try to get them to change specs so that alternate bids could qualify. We haven't had too much success, but I think we are beginning to make some headway."

In a series of copyrighted articles in the Norfolk Ledger-Star, former InterRoyal sales representative David Mosteller has been quoted as saying that InterRoyal benefited from close relationships with purchasing officials that included regular gifts by him to key state employes.

InterRoyal general counsel Walter A. Stein denied the charges attributed to Mosteller. "There is no foundation in fact or in law to his statements," Stein said. "Our success in Virginia is the result of 25 years of satisfactory service and the knowledge of hospital and college officials that our furniture holds up under the abusive treatment that it gets in their institutions."

Mosteller could not be reached for comment.

InterRoyal, which employes about 2,000 workers at a half-dozen plants across the country, makes office furniture and shelving. Stein confirmed a report that the privately owned company has an annual sales volume of $40 million to $50 million, but he said he was unable to break down the amount of business InterRoyal does with the state of Virginia.

Stein said that company executives have met with representatives from the state attorney general's office and that state police investigators have visited the company's Park Avenue headquarters in New York City to examine sales documents in connection with the probe.

Stein said he had no knowledge of the FBI investigation, but special agent William C. Ervin of the FBI's Richmond office said the investigation is only a few days old and that InterRoyal will be part of it.

Ervin refused to rule out the possibility that the investigation would involve elected officials."How can you say what it will involve when it isn't finished?" he said. But he said it does not necessarily involved political corruption.

Brooks said he has knowledge of gifts to his employes by private companies trying to do business with the state, but said he issued a directive banning acceptance of such gifts shortly after he took charge of the agency.

"I put out a regulation that absolutely nothing should be accepted," he said. "I don't have complete control over the actions of 150 people, but to my knowledge the directive has been followed." Brooks said that Mosteller was no longer representing Inter-Royal when he became director of purchase and supply.

G. Lloyd Nunnally, director of the purchasing agency from 1958 to 1970, acknowledged yesterday that Inter-Royal has paid him $150 a month for consulting services since shortly after he retired as director. While he was being paid by Inter-Royal, Nunnally served as a member of the board that hears appeals of contract awards.

"I was not aware of this situation until after Nunnally resigned from the appeals board," Brooks said. "But I can tell you he had absolutely nothing to do with purchases from Inter-Royal since I have been here."

The charges of favoritism to printing companies grew out of complaints by other printers in the Richmond area and are being investigated by a General Assembly subcommittee.

Brooks declined to answer those charges in an interview. "We have spent 27 man-days auditing these printing contracts and will discuss them in detail before the subcommittee on Tuesday," he said.