Metropolitan Washington's life support system, which feeds mainly on federal dollars, is due for its annual autumn transfusion. This one will boost monthly government-military payrolls by a minimum of $60 million.

Although President Carter hasn't made it official yet, experts believe he will approve a 7.05 per cent pay raise next month for the 300,000 civil servants, and 60,000 military personnel here. Nearly everybody in government will get those raises except for top career and political officials at or above the $47.500 pay level.

For the military, the raises will be effective Oct. 1. Civilian federal workers will see the before taxes increase in lat October or early November, since the raises for them are effective with the first pay period on or after Oct. 1.

The 100,000-plus retired federal workers and military personnel here also will get slightly fatter checks in October, as the result of a cost-of-living pay raise unrelated to the regular boost for active duty people. That 4.3 per cent raise was effective Sept. 1 (the second cost-of-living boost this year), but it won't show up in pension checks before October.

On Oct. 12, government mechanics, carpenters, laborers and other blue-collar employees will get their annual catchup-with-industry adjustment. The amount hasn't been fixed yet by Defense, which handles blue collar pay for the Washington area. But some experts predict it will be about 6 per cent, although this is only a guess.

Those increases are expected to boost the monthly federal payout to active employees, the military and to active employees, the military and retirees here by about $60 million a month. All in all, about 582,000 people here will get some kind of pay or pension adjustment.

Pay planners except President Carter will announce the exact amount of the military-white collar federal raise this week. And Defense will wait until about a week before the Oct. 23 effective date before spelling out the raises that will go to blue collar workers.