Calvert County is asking for mentions in public schools' PTA newsletters.

Charles County plans to present sample questionnaires at senior centers.

And St. Mary's County officials used their county fair to hand out fliers and refrigerator magnets bearing the slogan: "This is your future. Don't leave it blank."

The tactics are efforts by Southern Maryland jurisdictions to ensure their residents are counted in the upcoming U.S. census.

April 1 marks the official start of the effort, which is undertaken every 10 years to count the population of the United States.

The statistics gathered during the census help determine the boundaries of districts for the House of Representatives, the Maryland General Assembly and local political offices.

The numbers also help determine the yearly allocation of $158 billion in federal grants and play a role in decisions about where to build roads, schools and businesses.

In Southern Maryland, the 1990 census found 228,500 people. County and state officials later estimated that figure left out 4,088 people.

State officials say each person not counted costs $1,035 annually in federal funding, which would mean that the census undercount cost Southern Maryland $4.2 million a year.

Partly because such sums are at stake and partly as a matter of pride and civic responsibility, local elected leaders say they want to ensure as complete a count as possible.

"That activity is much appreciated by a political person, whether they're local, state or national," said Charles County Commissioner Marland Deen (R-Waldorf). He spoke Wednesday during a ceremony in Waldorf marking the start of a heightened campaign for census participation.

Deen read from a commissioners' proclamation that called for residents to respond to the census "to ensure our county and its citizens receive their fair share of federal and state funds."

"We're going to find every one of us," Deen said. "We will have a better handle on the makeup of our community."

In all three counties, officials have formed so-called complete count committees. Part of their role is to encourage households to return census forms that will be mailed beginning in March.

During the 1990 census, the three Southern Maryland counties had the Washington area's lowest rates of response to the questionnaires.

In Calvert County, 54 percent of households returned the form. The corresponding figure for St. Mary's County was 57 percent, and for Charles County, 65 percent. The U.S. average was 65 percent, and the Maryland average was 70 percent.

The Census Bureau sends workers called enumerators out to conduct interviews at households that do not return questionnaires. This year, about 1,000 people will be hired temporarily to help with the census. Even so, many people are not counted--either because they are not reached during the enumerators' three visits or because they decline to participate.

Nationally, those not counted are more often the poor and minorities--populations that might benefit from assistance programs that are distributed partly on the basis of census figures.

In Southern Maryland, parts of Nanjemoy and Indian Head in Charles County ranked among the areas in Maryland that were most difficult to enumerate during the 1990 census, according to the Maryland Office of Planning. No areas of Calvert or St. Mary's were ranked among the most difficult.

Charles County officials are aware of the undercounted areas and are focusing efforts to reach them, said county spokeswoman Nina Voehl.

"We hope that all our efforts will pay off and we'll have a complete count--100 percent," Voehl said. "Fill it out so we won't get left out."