Uncle Sam's million white collar workers would be due a pay raise of only 2.1 percent this October, 7 percent in 1982 and another 7 percent raise in the fall of 1983 if President Reagan's pay reform proposals were in effect now.

The administration has adopted the controversial pay reform plan first proposed by President Jimmy Carter. But it has proposed new changes in the formula that the government would use each year when it compares compensation with the private sector.

President Reagan's budget calls for a maximum 4.8 percent this year for government scientists, secretaries and other "classified" of white collar workers. Officials stress that the 4.8 percent is a maximum figure, and that changes in the economic situation, or pressure from Congress, could lower the amount.

Under the Reagan plan, the government would broaden its salary survey to include the value of not only pay, but also other fringe benefits -- leave, holidays, insurance among them -- to arrive at a TCC (total compensation concept). The value of the total government compensation package would be compared with similar packages in the private sector.

Included for the first time in the compensation match-up would be pay and fringe benefits of 12 million state and local government workers. Federal white collar salaries would also be geared to the going rate in private industry in about 135 geographic wage areas, much in the same way salaries are set each year for the government's half millioin wage board (blue collar) workers.

The big change in the Reagan reform plan would set federal pay at 94 percent of the comparable private industry level. The theory is that government fringe benefits exceed those outside government, that tenure, the portablility of federal pension systems (within government) and fully indexed cost-of-living raises give U.S. workers the edge over people who work for General Motors, GEICO, Goodyear and other firms.

Under the current federal-industry salary comparison system, pay (but not fringe benefits) is compared each year, and an "average" October federal pay raise is recommended to the president by a panel of advisers. He can accept that raise -- the so-called comparability figure -- in which case it goes into effect automatically.

If the president decides to lower it, he must send an alternative plan to Congress. Unless Congress rejects that lower, alternative plan (and it rarely does), it goes into effect instead of the higher, "comparability" raise.

Because pay has been held down in the past, federal workers are now said to be 13.5 percent behind their industry counterparts. The average federal white collar salary nationwide is in excess of $21,000 per year.

Reagan aids (as did the Carter people before them) concede that U.S. workers are behind according to the current measurement system. What they challenge is the validity of the system itself. That is what Carter, and now Reagan, want to change.

The Reagan plan is to implement pay reform over a period of three years. If the system were fully operational today, they say, federal workers this October would get only about 2.1 percent.But they figured that amount is too low, that it is too big a jolt for the already-shaken bureaucracy to take this year, so they set an arbitrary figure of 4.8 percent for the October raise.

The amount of the October raise won't be official until late August. There is pressure in Congress to shave the 4.8 percent. The Senate Budget Committee two weeks ago voted 6-to-6 on a proposal, by Sen. Charles Grassley, (R-Iowa) to defer any federal pay raise for 1981. Because the Grassley proposal was an amendment, it required a majority vote, so the 6-to-6 split killed it. But it shows that half the Budget Committee was ready, and willing, to cancel any raise this year. If that feeling indicates the mood of Congress, it could spell trouble for any kind of government pay raise this year.