Sometime within the next 25 days President Carter is expected to sign an executive order that will direct federal agencies to begin paying their 1.2 million white collar civilians 7.05 per cent more, beginning in October. Military personnel will also get the 7.05 per cent average, a before taxes increase.

But until Carter signs on the dotted line, that 7.05 per cent boost is not official. And there is the possibility - however slight - that he might go with a different amount.

Under the complicated federal pay-fixing law, government workers are supposed to be paid salaries that are comparable with similar jobs in private industry. The President is the ultimate judge of what is "comparable." He makes his decision based on data supplied by the Bureau of Labor Statistics, and recommendations from the Civil Service Commission and the Office of Management and Budget.

Once a federal-military pay figure gets printed, or reported on radio and TV, many people assume that is it. But it isn't necessarily so.

President Carter still has the power and authority to recommend a difference raise, or to give some grades more than others. And if he does it in the name of "comparability," that raise is automatic. It goes into effect Oct. 1.

Only if the President decides to deviate from "comparability," (a term nobody can actually define) does he have to go to Congress. If he submits a pay proposal that is less than "comparability" or asks for the raises to be delayed, he must get approval from Congress. If Congress upholds an alternate plan, it goes into effect. If Congress rejects the alternate plan, then the "comparability" formula is automatically put into effect.

There is no real reason to believe the White House will authorize anything other than the 7.05 per cent average raise. But until it is official, there is also no real reason people should plan on it or spend it.

Locally, about 3 of every 4 of the area's 350,000 federal workers will get the raise in October. Postal employees (who are covered by their own contract) aren't included. Neither are wage board (blue collar) workers, although in the Washington metro area they will be getting a separate pay raise based on local blue collar salary scales in industry. Federal and military retirees also will be getting an October adjustment but this is a 4.3 per cent raise, and it is based on cost-of-living.

Federal officials have worked up a new government pay scale, based on the 7.05 per cent amount. But, as one pointed out, it still isn't official and if the White House changes the amount, or staggers the raises among grades, all it takes is a change in the computer to revise the scales.

Assuming the Oct. 1 increase goes into effect at the 7.05 per cent rate, this is what the new federal pay scale will look like. The figures below show the minimum and maximum range for each grade:

Grade 1, 6.219 to $8.082 . . . Grade 2, $7,035 to $9,150 . . . Grade 3, $7,930 to $10,306 . . . Grade 4, $8,902 to $11,575 . . . Grade 5, $9.959 to $2.947 . . . Grade 6, $11,101 to $14,431.

Grade 7, $12,336 to $16,035 . . . Grade 8, $13,662 to $17,575 . . . Grade 9, $15,000 to $19,617 . . . Grade 10, $16,618 to $21,604 . . . Grade 11, $18,258 to $23,739 . . . Grade 12, $21.883 to $28.444 . . . Grade 13, $26.022 to $33.825 . . . Grade 14, $30.750 to $39.975 . . . Grade 15, $36.171 to $47.025 . . . Grade 17, a flat $47.500 and Grade 18, also a flat $47.500.

The so-called supergraders (GS 16, 17 and 18) will get little or no increase because Congress has ordered that the career, $47.500 pay rate remain in effect until late, 1978.