The Fairfax County Board of Supervisors yesterday called for a criminal investigation and an audit into allegations of improprieties and mismanagement in the country's $50-million-a-year contracting agency.

The country's prosecutor, who will conduct one of the probes, said that Virginia laws on the subject are so weak that it is unlikely he will be able to prosecute anyone.

"If they give me the same cases they've already told me about, there won't be a thing I can do," said Commonwealth's Attorney Robert F. Horan Jr.

The supervisors, despite some misgivings, voted unanimously for the investigations following charges by the county's chief purchasing agent that improper bidding procedures and cost overruns are routine in the county.

Several supervisors openly were skeptical of charges by Charles J. Cedeno, who last week was asked to resign as a result of what county officials called "gross and extremely vulgar conduct" toward his subordinates.

"It should be clear that this [Cedeno's allegations] is just a smokescreen," said Supervisor Marie B. Travesky (R-Springfield). Cedeno was placed on administrative leave with pay yesterday pending the outcome of the investigations.

Among Cedeno's charges were claims that a contract for landfill dirt was improperly extend to a $2 million award; that the county's circuit court clerk purchased $60,000 worth of equipment without competitive bidding; and that two county supervisors ignored purchase rules in buying office furniture.

Horan said yesterday that an earlier review by his office had turned up some technical violations of purchasing procedures, but he said those violations were not prosecutable under state law. Both Horan and County Attorney David Stitt declined to specify the source or nature of those violations.

Some of the cases, Horan said, could not be prosecuted because they involved elected county officials, who are not required by law to follow official channels in making purchases with county funds. The rest of the cases, he said, were not pursued because they were older than Virginia's one-year statute of limitations.

"As a layman, I think some of those purchasing practices should be redrafted," Horan said. "I'm not sure anybody is clear on when competitive bidding should be sought."

In approving the call for the investigations, the eight supervisors at Yesterday's meeting stressed their belief that any irregularities were the result of ignorance -- not fraud or corruption.

"I don't think anyone in this county says we're perfect and don't make mistakes," said Board Chairman John F. Herrity, a Republican. "But when we find a problem exists we address it openly and candidly and take actions to correct it."

In a report to the board yesterday Acting County Executive J. Hamilton Lambert said he had issued a memorandum last week instructing county staff members to abide by purchasing laws and regulations after he learned of the results of Horan's earlier review.

Lambert did not seek to reprimand or discipline anyone. "What could you do?" he asked yesterday. "There appeared to be no intent to defraud. The first thing to do was to say cease and desist in this [improper] practice."

Supervisor Sandra L. Duckworth (D-Mount Vernon) said she "just simply did not know" about conty purchasing procedures when she directed an aide to purchase three secretarial chairs for $400 several months ago.

"This does raise questions about the whole purchasing process," Duckworth said, "because I certainly didn't know and nobody ever bothers to tell you. Everyone assumes you know. Maybe others are in the same boat."

Cedeno, meeting with reporters after the board's decision, praised the call for the investigations but rejected assertions by supervisors that they were unaware of purchasing procedures. "They make the rules," he said. "They ought to know what they are."

Cedeno expressed surprise that Horan already had investigated some of the possible irregularities.He said county officials had not informed him of the probe and no one from Horan's office questioned him. "I never knew there was an investigation conducted at all," Cedeno said.

The purchasing official said that he had been the object of frequent harassing telephone calls from county employes and repeated his charge that county officials were trying to reform purchasing practices and see that all major county contracts are subject to competitive bidding.

He said yesterday his boss, Fred K. Kramer, director of the county's general services deaprtment, had warned him against pursuing claims of purchasing irregularities for fear of "ruffling the feathers" of elected officials. Kramer denied the charge and said that officials had pursued all of Cedeno's charges "to the n-the degree."

While Lambert did not specify the charges that led the county to seek Cedeno's resignation last week, several county officials said they had been advised that Cedeno had been accused by several female staff members of making an inordinate number of crude remarks and cursing in the office.

County officials said that they moved this weekend to lock Cedeno out of his office on the sixth floor of the Massey Building, charging that he had removed county documents without authorization.