Unless the economy takes a substantial nosedive, white-collar civil servants and military personnel will probably get a 7.05 per cent pay raise - their biggest boost in years - effective Oct. 1.

For most of the 300,000 Washington area white-collar civilians, the extra money will show up in paychecks received in early or mid-November. The 100,000 military aides stationed here and nearby would get comparable pay raises. Postal workers, blue-collar federal civilians and government-military retirees are not included in this catch-up-with-industry adjustment. Most D.C. government employees would probably get equivalent increases.

The pay raise, which has a $3.5 billion price tag, is more than a half per cent above the civilian-military pay increase budgeted by either the Ford or Carter administrations for 1977. It is also higher than the 6.9 per cent average pay increase the Labor Department recorded for private industry workers during the 12-month period ending in March.

The pay raise isn't official - nor the amount set - until President Carter signs on the dotted line sometime late in August. But agreement on the 7.05 per cent figure by Carter's chief pay advisers makes it virtually a sure thing.

The 7.05 per cent catch-up-with-industry amount was approved by the Civil Service Commission and The Office of Management and Budget. Both CSC and OMB act as the President's chief in-house advisers on federal-military pay in the complicated system used to adjust government wages each October.

By law, federal salaries are supposed to be those equal to those in private industry. To establish and maintain parity, Congress set up a system years ago calling for annual October adjustments for the 1.2 million white-collar government workers and the nearly 2.6 million military personnel.

To determine what is happening in industry, government specialists from the Bureau of Labor Statistics make annual wage surveys (usually of a 12-month period ending in March) and give that data to the President's agents early each year. The agents, in consultation (but rarely in agreement) with employee unions came up with a recommended "comparability" figure for the President.

The President can simply accept the comparability increase. The raises - which Congress cut itself in on last year and will not get this year - go into effect automatically by Oct. 1 unless killed or modified by either the Senate or House.

If however, the President chooses to modify the pay increase, or to delay it (as both Nixon and Ford did) Congress must approve that alternate plan. Otherwise the original "comparability" figure automatically goes into effect.

The White House has indicated that Carter will go with the 7.05 per cent raise unles economic conditions got so serious that he had to slap wage-price controls on all segments of industry and government.

Last October, federal workers and military personnel got an average 4.83 per cent pay raise. The amount was not across-the-board (as the upcoming raise will be). Employees in Grade 5 got as little as 4.24 per cent, while some Grade 15 aides got 7.92 per cent, in 1976.

Presidential advisers would have preferred a sliding scale increase this October - to make salaries more comparable to industry. They wanted raises that would have ranged from 6.26 per cent at Grade 7 to between 11 per cent and 14 per cent for top career civilians. But unions opposed that plan, so the across-the-board raise was approved by the pay agents.

Federal executives making $47.500 will not get any October 1977 pay raise. Nor will they be able to "catch up" with this increase in the October, 1978 pay raise.

Congress voted to keep the $47.500 lid (after members of Congress got a $12,900 raise last March) so senior civil servants in Grades 16, 17 and 18 will have to sit out the October pay raise. Others will get only token increases to bring them up to the $47,500 maximum.