City and county administrators in charge of most of the area's 71,000 local government workers have endorsed a White House plan to reform methods Uncle Sam uses to set pay raises for his 300,000 white collar workers here. The changes would probably mean smaller future pay raises for Washington area civil servants, who now average $22,000 a year.

The backing of the city-county administrators, through a special committee of the Council of Governments (COG) puts them at odds with most local politicians who depend on employes from the area's dominant industry -- the federal government -- to stay in office.

Along with federal unions, and many rank-and-file federal workers, the politicians believe the Carter Administration's "reforms" are designed to produce data that will produce smaller future raises for U.S. workers.

Endorsement of the controversial federal pay shakeup plan came in a letter from A. Douglas Harman, Alexandria's city manager, to Alan K. Campbell, head of the Office of Personnel Management. Harman heads the city-county administrators group at COG. Campbell is President Carter's chief personnel adviser and the prime mover behind federal pay reform.

Members of the COG group are in charge of personnel programs for the District of Columbia and the counties of Arlington, Fairfax, Loudoun and Prince William in Virginia, and Prince George's and Montgomery in Maryland. Cities represented are Alexandria, Bowie, College Park, Falls Church, Gaithersburg, Greenbelt and Takoma Park.

Harman, the Alexandria city manager, said local governments have trouble getting and keeping top-quality workers because the federal government pays "much more" for people doing "essentially the same work."

"We're so far behind," Harman said, "and now the federal government goes zooming off into the clouds with a 7 percent pay raise! We're closer to the people than the federal government," he said, "and we have to answer for these things."

Many are local governments limited pay raises for employes this year to 5.5 percent as requested by the president. Last week, the president announced a 7 percent raise for federal workers, citing "economic conditions."

"The way the federal government handles its pay has a devastating effect on most local governments," according to Harman, even in Washington's most affluent suburbs. He said he expected the president's pay reform would make local governments "more competitive" with the federal government.

Campbell has been meeting with groups around the nation trying to drum up support for pay reform in the same manner as the administration sold its civil service reform last year. He met with the COG group a couple of weeks ago and outlined the pay-reform proposal. City-county managers checked with their own personnel people and then endorsed the proposal.

Most experts believe the pay reforms would shave the amount of future federal pay raises for many employes. Federal officials this year said it would take a 10.4 percent raise to bring government pay up to levels of industries surveyed.

Carter's plan would broaden the survey and bring many more low-paying jobs into it. It would set local rates (based on industry pay) for half-a-million nonprofessional federal workers and count the value of federal fringe benefits, such as annual leave, holidays and retirement, in comparing "total compensation" with industry.

One of the major recommendations of the Carter plan is to begin comparing federal pay rates with those of the nation's 12 million state and local government workers. Their pay and fringes are excluded from federal vs. industry wage studies. Critics say this has resulted in "inflated" pay recommendations each year for federal workers, since generally lower local government wages are not studied.

The Carter plan is expected to draw fire from the AFL-CIO's Public Employe Department, which opens its convention today at Dupont Plaza. PED represents federal and postal unions that have accused Carter of mounting an "antibureaucrat" campaign to win votes and draw attention from economic problems.