Picture 1, Members of the Arlington Committee for a Fair Count discuss ways to help federal census takers get an accurate count of residents; Picture 2, John G. Milliken, head of the Arlington Committee for a Fair Count; Photos by Craig Herndon -- The Washington Post

The army of federal census takers won't begin their national head-counting campaign until April 1, but officials in Northern Virginia already have begun softening up the local terrain.

Committees have been formed and civic associations recruited to bombard communities with a direct command. When the National Census commences -- step forward and be counted.

The local effort is prompted neither by patriotism nor a desire for mathematical precision. Money and political power are at stake. Since funding and representation at both state and federal levels are apportioned largely according to population, the results of this year's census will directly affect Northern Virginia's fortunes for the next decade.

"What we're talking about here is big bucks," says George Colyer, the chief of comprehensive planning for Alexandria.

In Alexandria and Arlington County, Complete-Count Committees have been commissioned by local politicians to trumpet the census. Their primary targets are minority groups such as blacks and foreign-born residents who traditionally have been leery of filling out forms and avoided the process in larger proportions than the rest of the population.

"We have to work with them to quiet their fears," says John Miliken, a former assistant to Rep. Joseph Fisher (D-Va.) and the coordinator of the Arlington Fair Count Committee. "The census shouldn't be seen as something threatening; 60 percent of our job will be publicity."

Local officials are hoping the results of this year's census count will provide them more political punch, since the totals will be used as a basis for reapportionment in the House of Representatives as well as in the state's General Assembly. They also are hoping the figures will bolster their side of a long and bitter argument with the state.

Almost since the last census in 1970, Arlington, Alexandria and Fairfax have been claiming higher populations than those estimated by the state.

"We're about 7 or 8 percent higher," says Jeff Bates, a research analyst for Fairfax County. Fairfax filed a formal challenge to estimates prepared by the Tayloe Murphy Institute (TMI) at the University of Virginia.

In Arlington, for example , TMI estimates there are currently 149,400 residents. The county's planning office claims a figure of 163,146, a difference of more than 13,000.

To determine how much that difference of opinion is costing Arlington, county planners are currently compiling a list of all state and federal programs that use population as a component of the funding formula.

"It's more like a booklet than a list," says Arlington planner Terry Russell. The programs, which number more than 100, include funds for education, law enforcement assistance, health and housing.

The difference is estimates is the result of the different methods used to formulate them. Local jurisdictions use a relatively simple formula which multiplies the average household size, determined regionally by a school census survey in 1977, by the number of existing housing units, minus the vacancy rate.

The state employs three seperate methods that rely upon birth and death rates, state and federal income teax returns and school enrollments. TMI then takes the average of the three surveys.

Both sides claim the other's methodology is muddled. Officials at TMI, which has been under federal contact to provide state estimates since 1967, argue that localities regularly overestimated both the average household size and the number of housing units.

"Northern Virginia is more prone to complain," says William Serow, director of research at TMI.

Northern Virginians counter that TMI formulas depend too much upon school enrollment, which has been dropping by more than 4 percent in the area for the last five years.

"Even though we're losing school enrollment, we're gaining a hell of a lot of singles and childless couples," says Colyer of Alexandria. "In the 1970 census, Alexandria had a population of 110,900. Tayloe Murphy says we have only 104,700 now, while we say 116,900. In other words, they're showing a slow decline, while we're showing a slow growth."

Serow admits that a large increase in the number of singles and childless couples living in an area presents a problem: "We don't know at the moment how well our methods deal with that kind of fundamental change."

But Serow will not apologize for TMI's methods: "We'll know how accurately our methods work in about a year."

The U.S. Census Bureau admits the results of its census cannot be perfectly accurate. In 1970, the bureau estimates it missed 5.3 million people representing 2.5 percent of the population.

This time, however, the bureau is hoping to cut that uncounted figure by spending more than four times as much as the $221.6 million cost of the 1970 count. Much of that money will be spent trying to reach foreign-born residents and other minorities such as blacks, who were missed by a rate of 7.7 percent compared to a rate of 1.9 percent for whites.

Northern Virginia officials are anxious that the federal effort not fail. If the final local count is closer to their own estimates than TMI's, it could provide a basis for seeking federal and state funds for past years. It could also mean that in the coming decade, their own methodology would supersede the present state ones.

"If the demographer types like Tayloe Murphy are off considerably, their credibility is going to be questioned," say Colyer. "I would assume they would beat a hasty retreat."