Uncle Sam will shove 15,400 new bodies into his already overcrowded executive salary deep freeze next month. While most of the government's white-collar workers will be getting a 4.8 percent raise, their rapidly growing number of chiefs at the $50,112.50 pay range will watch, again, from the wings.

Because of the $50,112.50 pay cap imposed by Congress the number of top-salaried U.S. executives has been growing like a rabbit ranch. Today 34,800 employes -- in Grades 15, 16, 17, 18 and the Senior Executive Service -- bump the pay ceiling. This time next month it will dip down into GS 14 ranks. The number of executives at the top of the pay totem pole will jump to 46,200.

Congress has the option to ease the top pay compression problem. The salary limitation is contained in appropriations bills to finance Senate and House operations, and interested parties are working to have it stricken from the bills. If it happens, long-frozen U.S. executives could get a raise of at least 16.8 percent (amounts denied them in previous general federal pay raises) and could even be eligible for the 4.8 percent that their subordinates will get in October.

Senior Executive Association chief Jerry Shaw believes there is a "fighting chance" Congress will do something about executive salaries. The key, he feels, is whatever signals it gets from the Reagan administration. Many Reagan appointees -- who come from corporations where $50,000 a year is peanuts -- have been privately appalled at the "limited" salaries they can offer people they are trying to bring in, and keep.

Senate hearings are coming up on the pay issue (before the Governmental Affairs Committee). A lineup of Reagan administration officials who are favorable to executive pay raises has been assembled to testify. Senate and House leaders have said they would go along with an executive boost, but only if the White House gives them the green light.