The federal payroll amounts to about $1 million a month in each of nearly 300 medium-sized and small cities and towns across the country.

That fact won't be lost on Congress when it takes up President Reagan's proposal for a 5 percent across-the-board cut in federal pay. The proposal is part of the president's upcoming budget.

Because of the local impact of a federal pay cut -- and "local" is a lot of places, because 87 percent of the federal work force is employed outside of Washington -- the proposal will run into a lot of opposition from Congress, as well as the business community. The fires of that opposition will be fanned when politicians, merchants and bankers get out their calculators and estimate the possible damage pay cuts would have on their home towns.

Although most Americans think of Washington, D.C., when they think of the federal bureaucracy, the fact is that the U.S. civilian payroll exceeds $1 million a month in each of 272 cities and towns across the nation. In most of them it is much more than that.

A 5 percent cut in federal salaries could have a significant impact on the economies in other federal centers, ranging from giant cities such as New York (with 88,000 U.S. government workers) and Chicago (66,000 U.S. workers) to smaller, economically hard-pressed towns such as Pittsfield, Mass.; Altoona, Pa., and Cumberland, Md., all of which have monthly federal payrolls of more than $1 million.

Cutting federal pay is like eliminating unnecessary military installations. Everybody is for it in theory, so long as those cuts are made in somebody else's back yard. Members of Congress vote in the abstract to trim Army, Navy and Air Force facilities -- but fight to the death when the Pentagon announces that home-district bases are on the hit list.

The average federal salary outside of the Washington area is about $26,000 a year. Any town or city with 462 federal employes has a payroll of at least $1 million a month. That takes in a lot of places beyond the Capital Beltway.

Roanoke, Va., hardly a metropolis and rarely on anyone's list of major federal centers, has 3,200 federal workers. Eau Clair, Wis., has more than 500 federal civil servants. Erie, Pa.; Flint, Mich.; Lancaster, Pa.; Greenville, S.C., and Worcester, Mass., have about 1,400 federal employes each. Hagerstown, Md., has a federal payroll of nearly $1 million a month.

Cities with 10,000 federal workers include Anaheim, San Jose, Sacramento and Bakersfield, Calif.; Columbus, Ohio; Rock Island, Ill.; Long Branch-Asbury Park, N.J.; Milwaukee; Portsmouth, N.H., and Tampa, Fla.

Cities with more than 20,000 U.S. workers -- and the huge payrolls they bring in -- include Dayton, Ohio; Houston; Honolulu; Kansas City, Mo.; Newark; Oklahoma City and Seattle-Everett.

Cities with between 30,000 and 40,000 federal workers are Atlanta; Dallas-Fort Worth; Boston; St. Louis; Denver; Norfolk-Virginia Beach, Va.; Salt Lake City; San Antonio, and San Diego.

San Francisco, Los Angeles-Long Beach, New York, Chicago and Philadelphia have well over 50,000 federal workers each.

Check out the home towns of members of the Senate and House Budget and Appropriations committees, and you will find only a handful of members who do not come from major -- to them -- federal centers.