Fairfax County Board Chairman John F. Herrity complained to a Senate subcommittee yesterday that the Justice Department has unfairly used a "battering ram of punitive action" in pressing his county to end alleged discriminatory hiring and promotion practices.

Speaking before Sen. Orrin G. Hatch (R-Utah) at hearings on affirmative action, Herrity declared that despite a federal court order to end hiring discrimination, "any reasonable person looking at Fairfax County's employment data would conclude that it has not performed in a bigoted or biased manner . . ." The court's finding of discrimination is being appealed.

The county, Herrity said, is "willing to sit down and work things out," but "there is something despotic in the force generated by the [department's] civil rights division . . . which can force Fairfax County into humiliating procedures which can finally result in the possible expenditure of millions of dollars of taxpayers' monies."

Hatch, chairing the Senate judiciary subcommittee on the Constitution, was receptive to the argument. After listening to Herrity's testimony, he said court sanctions against the county seemed examples of "onorous, burdensome, governmental repression -- at least the way you're explaining it to us."

The Justice Department has been pressing its discrimination suit against the county since 1978. The following year, U.S. District Judge Albert V. Bryan Jr. largely rejected the government's case, but an appeals court ordered a new trial.

Justice based its charges on 1977 statistics that showed in part that only 5.6 percent of 7,000 workers employed by the county at the time were black, compared to at least 24 percent of the work force in the metropolitan area.

At a retrial this spring, Bryan reversed his earlier ruling. His decision made hundreds of blacks and women who applied for but did not get jobs in the county government eligible for back pay if the county cannot prove that they were not qualified or others were equally or better qualified.

Throughout the long legal fight Herrit has been outspoken in his condemnation of the Justice Department. Early this year he sent letters to President Reagan and Attorney General William French Smith urging them to drop the matter on the basis of Reagan campaign pledges to end harassment of local officials.

Herrity said yesterday that, in 1979, 64.9 percent of all para-professionals hired by the county were female. In 1980, he said, that figure rose to 77.3 percent. Even so, he said the future of the county's latest appeal is less than bright. "We can expect to have no relief with the courts, for they are bound by a decade of precedential decisions which now offer little leeway in final judgment making," he said.