A rail mechanic for the Washington Metropolitan Area Transit Authority, angered that he was ordered to work the July 4 holiday, refused to cash his $222.60 pay check and instead donated it to Fairfax County.

The mechanic, Harold E. Malone, charged that Metro overstaffed the Alexandria Rail Car Yard by as much as 75 percent, although there was not much work to do that day.

John F. Herrity, chairman of the county's Board of Supervisors, yesterday called mechanic Harold E. Malone "a Metro employe with a lot of guts" and said the mechanic "put his money where his mouth was." He said full staffing was "typical" of Metro. "You've heard of Orwellian," he said. "Well, I think this is 'Metro-wellian.' "

Metro spokeswoman Beverly Silverberg declined to respond to Herrity's charges but defended the transit service's work policies. She said a full crew was needed to stand by at the Alexandria yard on July 4 because of extended rush hour schedules and an extraordinarily large number of passenger trips -- 540,000, as opposed to 400,000 on a normal weekday.

Malone, who lives in Fairfax County, had asked that his check be returned to the Metro operating budget or donated to Herrity's favorite charity. Herrity ordered the money deposited in the county's general operating fund, where it will offset to the tiniest degree Fairfax's $30 million share of Metro's $200 million budget for fiscal year 1986.

Malone was at work yesterday afternoon and could not be reached by telephone. In a letter accompanying his check, however, he said Metro could have saved money by having only 10 to 12, instead of 40, workers on duty to handle emergency repairs.

As it was, there was not enough work, Malone continued, and "about half of these skilled craftsmen were assigned to scrubbing and painting floor jacks at double-pay. The other half stood around; sort of like waiting for a train, I guess."