Uncle Sam's one million white-collar civilians may be headed for an October pay raise in the neighborhood of 7.8 percent instead of the 6.2 percent boost originally budgeted by President Carter.

For the typical Washington area civil servant whose average salary, according to the government, is now $23,494, a 6.2 percent raise would mean a before-taxes increase of $1,457. The 7.8 percent raise would boost the white-collar pay average to $25,327. There are about 300,000 white-collar civilian workers here.

The 7.8 percent October pay estimate comes from a mid-year review and reestimation of the fiscal 1981 budget. It was released yesterday by the Office of Management and Budget. OMB now projects an October 1980 white-collar raise of 7.8 percent, and sees a 9 percent increase due in the fall of 1981 based on current economic assumptions.

The higher figure for the 1981 fiscal year (it begins Oct. 1) is based on adjustments for inflation, and conparisons of federal pay-fringes against total wage package gains in the private sector between March 1979 and March 1980.

President Carter's original estimate of 6.2 percent presumed that Congress would approve major federal pay "reforms" he wants.

Under pay reform, which appears unlikey to clear Congress this year, the government would change the yardsticks it uses to compare federal vs. industry salaries. It would use a "total" compensation" concept that would weigh the value of U.S. salaries and fringe benefits (such as leave, holidays, retirement and insurance) against wages and benefits in industries surveyed. Currently, federal pay is based on straight salary comparisons with similar jobs in private industry.

Based on wage data gathered by the Burea of Labor Statistics, salaries in the private sector are up an average of 9.1 percent in the March 1979-March 1980 measurement period. The cost of living during that 12-month survey time was up more than 14 percent.

Officials say the new, higher estimate of 7.8 percent for the October 1980 federal pay raise are based on the total compensation concept as envisioned by pay reform.

Federal union leaders were quick to react to -- and attack -- the new budget figure of 7.8 percent.

Kenneth Blaylock, president of AFL-CIO's American Federation of Government Employees, said, "We're looking for what the private sector got, and the private sector wage movement this year has been in excess of 9 percent."

James M. Peirce, president of the independent National Federation of Federal Employees, said the new higher estimate is "a political decision; we just wish the president had come closer to what is right than a 7.8 percent raise."

Under the law, President Carter will not make his pay proposal known to Congress until the last week in August.

President Carter does have the authority to recommend an "alternate" plan to Congress that would give federal workers less than a full comparability catch-up with industry Congress has 30 days to veto that alternate plan. Otherwise, it will go into effect automatically.

In the unlikely event Congress overruled the president's lower alternate pay plan in favor of a higher catch-up-with-industry amount it could order the higher pay raise into effect. Either way, white-collar workers would get an adjustment effective in October.