Private industry pay is up an average of 6.9 per cent, according to the primary economic yardstick the Carter administration will use to determine the amount of an automatic October salary increase for federal and military personnel.

An increase of that magnitude, if applied to the government sector, would cost nearly $3.5 billion.

Insiders say the new salary data from the Bureau of labor Statistics make it almost certain that white-collar civil servants and military personnel will get a minimum 6 per cent (maybe more) raise this fall to bring them in line with their private industry counterparts.

Locally there are 300,000 white-collar civilians who will benefit from the as yet undetermined October pay raise. It would also go to the nearly 100,000 military people stationed nearby. Postal employees, federal blue-collar workers and government retirees will not be included in the October pay adjustment.

It will be mid-August before the President's pay agents (the Civil Service Commission and the Office of management and Budget) translate all available private vs. federal pay data into a pay proposal for President Carter. If he accepts their figure the raises go into effect automatically with the first pay period on or after Octo. 1.

If President Carter decides to lower the amount of the pay raise suggested by his agents, or chooses to delay it for some reason beyond Oct. 1, he would have to submit an alternate plan to Congress by sept. 1. Government employee unions have been privately assured, however, that Carter will not tamper with the timing or the amount of the catch-up raise when it is finally decided, unless there is a national emergency, or wage controls are placed on all segments of the economy.

Although the 6.9 per cent figure from the BLS is good news for government employees and military personnel, it would be a mistake for them to count on that being the final amount.

Both Presidents Ford and Carter made "guesstimates" in their budgets that the October increase would be about 6.5 per cent. Congress also has had pay experts looking into the situation, and they've suggested that the catch-up-with-industry boost will be 6.3 per cent.

It will be weeeks before the BLS data is digested and translated into a "payline" comparing private and federal jobs, and before an average pay-raise proposal is worked out. The BLS study covered major private employees for the 12-month period ending last March.

Although President Carter has indicated he won't shave the raises, there is good reason to believe that, for both economic and public relations reasons, the government pay raise will be held to the absolute minimum that can be justified.

Federal pay raises aren't as popular beyond the beltway as they are in Washington. Most of us here either work directly for Uncle Sam or are in services or professions that are essentially pilot-fish operations for the government.

Cost is also a factor. Each 1 per cent increase in the federal-military payroll adds $500 million a year to the total price tag for the care and feeding of the people side of government.A 6.2 per cent raise across the board would cost $3.15 billion. If he raise is for the 6.5 per cent amount projected in Carter's budget, it would be worth $3.25 billion, and if workers got a straight match-up with private industry, according to the BLS data, the federal-military cost would be $3.45 billion.