Pro-Democratic government union leaders will have two regrets this October when their typical member gets hit with a $3.20 cut in the old paycheck. Those regrets are:

One, that it is happening!

Two, that they can't blame it on Ronald Reagan!

Since the Reagan administration took office, thousands of government workers have been fired for economic reasons, and cost-of-living raises for retirees have become less frequent.

Federal workers have been shaken by administration plans to raise the retirement age (this proposal has now gone with the wind) and by the latest plan (still very much up in the air) to link raises and job security to merit, rather than seniority. Some have been shaken so much that they have come to see the value of unions.

The Reagan folks--although they profess to hate only red tape and not federal workers--have made unions much more attractive to civil servants in the past couple of years. In fact, the president of one union said that "if Reagan didn't exist, we would have to create him."

But the latest flap--the recomputation of hourly federal pay rates--didn't come from the anti-federal worker White House. It came from government worker friends, Democrats on the House Post Office-Civil Service Committee.

Last year, while working on the budget, the full House ordered the committee to come up with substantial savings in federal pay or retirement costs. The committee balked at further cuts in pay or retirement benefits and, to make its savings quota, settled on a temporary bookkeeping change to go into effect this October.

Under the change, for the next two fiscal years the government will figure employe pay rates based on a year with 2,087 hours. Those rates now are figured on a 364-day year with 2,080 hours. When put into effect, the new system will on the average shave $3.20 from each employe's biweekly paycheck. That will save an estimated $240 million over the two years. The 2,080-hour computation formula will return in 1985.

The House committee, which didn't want to make any cuts in federal pay or benefits, figured the bookkeeping change was the lesser of evils. Maybe so. But federal workers howled last week when they learned that the change was coming and what it would cost them. It isn't so much the money, many said, as the pettiness of the thing.

Sen. Ted Stevens (R-Alaska) says he will try to get Congress to defer the bookkeeping change until January, when federal workers may get a 4 percent pay raise. If not, the pay cut will take effect in October.

Whenever it takes effect, it will be as the result of congressional action. The White House--this time--is innocent.