The 7 percent federal-military wage increase set for October will pump an extra $2 million a day into the pay checks of more than 400,000 federal workers, District of Columbia government employes and military personnel here.

President Carter's decision to set the raise at 7 percent represents a compromise between the 5.5 percent he had previously budgeted for government pay hikes, and the 10.4 percent figure his advisers say is needed to make white-collar federal pay comparable with private sector salaries.

The raised proposed by Carter will go into effect automatically unless Congress vetoes it and orders the larger 10.4 percent hike. That action is considered unlikely.

For the typical Washington-based white-collar government worker, who now earns more than $22,000 a year, the raise will be effective with the first pay period beginning on or after Oct. 1. The increase begins Oct. 1 for the military.

Federal "supergraders" already at the maximum $47,500 career pay ceiling will not know what raise, if any, they will get until Congress decides what to do about its own pay. By law salaries of Senate and House members are supposed to go up by the amount of the general federal pay increase.

However, it is believed that Congress will vote itself less, or decide to forgo a raise this year.If that happens, pay for top-level civil servants would remain at the $47,500 level for another year.

About 20,000 federal workers in the two lowest Grades -- GS 1 and 2 who earn $8,900 or less -- will actually get more than 7 percent. Administration officials decided to boost them by about 9 percent, because many of them are paid at or near the federal minimum wage already.

Under current law, most of the 40,000 District government classified workers will get the same 7 percent raise as their federal counterparts. Raises negotiated in the past by other D.C. workers, including police and firefighters, usually have worked out to about the same amount as those given federal and District white-collar employes.

The D.C. budget as approved by the Senate, and now before a Senate-House conference committee, carries funds to finance a 3 percent pay raise. The actual shortfall between funds tentatively approved and the amount needed to pay for a 7 percent increase is estimated at about $30 million.

Federal agency budgets approved or before Congress anticipated a 5.5 percent pay raise. White House officials said yesterday that Congress would be asked to approve supplemental funds to pay for part of the extra increase, and also that government departments would be required -- through other economics -- to absorb part of the additional costs.

The Carter Administration had requested $3.2 billion to cover a 5.5 percent pay raise. The 7 percent increase will add another 700 million to the cost of the federal-military payroll, which now runs in excess of $60 million a year.

Congressional employes are expected to get the same 7 percent pay raise. However, it does not cover federal, postal or military retirees who are due a second cost-of-living raise of 6.9 percent in October.

Also excluded from the federal-military pay raise are regular workers of the U.S. Postal Service and wage board (blue collar) federal employes.

The USPS negotiates separately on pay and fringes for its 600,000 rank-and-file employes. Rates for the half million blue-collar federal workers are set according to prevailing rates in local private industry, as determined by the government.