A federal investigator has cleared John V. Graziano, the Agriculture Department's inspector general, of all charges levied against him by a former USDA employe who had said Graziano had hired numerous "cronies and girl friends" after he was appointed by President Reagan.

K. William O'Connor, special counsel to the Merit Systems Protection Board, said that there is no evidence to support any of the charges made in April, 1982, by Stevie L. Carroll, who had worked for Graziano until voluntarily resigning last year.

"The bottom line in this matter insofar as prohibited personnel practice allegations are concerned is that Mr. Graziano had been publicly pilloried for alleged violations which are not supported, but refuted, by investigation," O'Connor said in a letter to presidential counsel Fred F. Fielding and Agriculture Secretary John R. Block.

After Carroll accused Graziano of misconduct, the White House asked Charles L. Dempsey, the inspector general at the Department of Housing and Urban Development, to investigate. His three-volume report said that "with one possible exception, it does not appear that overtly illegal actions took place."

But, Dempsey said, Graziano had shown "lapses of judgment" by offering several women jobs at social gatherings in a way that suggested "the job-related qualifications of the various women . . . may not have been the only concern motivating Graziano in his approaches to them." The women had told investigators that they believed Graziano expected sexual favors in return for a job.

Graziano denied those claims in the report but refused comment to reporters.

O'Connor said that his probe found "no credible evidence" of any misconduct by Graziano, who has been a government investigator for 32 years.