Montgomery County's inner suburbs, areas of rapid growth in the 1950s and 1960s, lost between 12 and 18 percent of their population in the last decade as housing construction slowed, grown children left home and high housing costs drove families with young children well beyond the Beltway.

Preliminary figures from the 1980 federal census show such communities as Bethesda, Silver Spring and Takoma Park following the path of cities like Baltimore, which began its population decline more than a decade ago. Baltimore itself, according to the preliminary data, lost 18.6 percent of its population since 1970, leaving it with 737,557 residents today.

While the count showed population drops in Baltimore and the inner suburbs, outlying areas such as Howard, Anne Arundel and Frederick counties grew rapidly. In Howard, Columbia pushed so far into the farmlands, it was the main factor in the county's 87 percent population increase.

The figures for several areas, most notably Prince George's County, were not yet available yesterday.

Preliminary Census Bureau figures started to arrive in local county planning offices last week, and immediately caused consternation in many areas -- particularly Baltimore City -- where local officials felt the figures fell far below actual population counts.

Their objections were more than just academic: Final census bureau figures become a basis for calculating the distribution of billions of dollars in federal grants, and no city or county wants to be shortchanged. Regional census officials in Philadelphia estimate each person counted means an average of $200 in federal funds, annually for a local jurisdiction.

In addition, census figures are the basis for redrawing the boundaries of congressional and state legislative districts.

Using those figures, Baltimore city, which Mayor William Donald Schaefer believes has a population of 818,000 would lose more than $16 million annually in federal funds if the census bureau's figures becomes the established count for the city.

"Mayor Schaefer thinks all those people are there, so we're trying to find them," Baltimore City Planner John Backer said yesterday. "We will have a long list of questions [for census officials] when we turn in our local view response," he added.

Even in jurisdictions that registered a substantial increase, such as Howard and Anne Arundel counties, local officials complained that the census takers had undercounted. "I am not in agreement with the figure at all," said Anne Arundel County Executive Robert Pascal.

According to the preliminary census data, Anne Arundel grew from 298,042 people to 359,565 -- a 20.6 percent increase -- but county planners believe the population in closer to 395,000.

In Frederick County, where Interstate Rte. 270 merges with highways going to Baltimore, Pennsylvania and West Virginia, the population rose by 31.6 percent to 11,748, with the most dramatic growth taking place immediately east and west of Frederick, in communities like New Market and Middletown.

Similar growth took place closer to Washington, in the northern parts of Montgomery County, where census figures showed the Gaithersburg area nearly trebling in population, from 23, 150 to 64,894. Further east, the Olney area just about doubled in size and now houses 23,773 persons, according to the preliminary data.

Montgomery County's entire population increased from 522,809 in 1970 to 564,507 today, according to the preliminary figures. A county planner said he believed there was a discrepancy of no more than 10,000 people between the federal preliminary figures and the county's own estimate.

The new figures for Montgomery and the rest of the state, bear out predictions about the decreasing size of American households. Overall, the figures show Montgomery County's household size decling from 3.3 to 2.77. Again, the smaller households tended to be clustered in the inner suburbs while bigger families lived outside the Beltway.

In some of the inner-Beltway communities, the number of housing units actually increased over the last decade, but the population declined. In the Bethesda-Chevy Chase election district, for instance, census takers counted nearly 4,500 more dwelling units than in 1970, but 12,300 fewer people, for a total population of 84,786.

In Takoma Park, the decline was more dramatic: while the housing stock increased by about 4 percent, the population declined by 18 percent, leaving the city with 10,261. In the Silver Spring-Wheaton election district, there were 14 percent more houses than 10 years ago, but 12 percent fewer people.

Even while the increases in housing stock, however, county planner Dale Price said that housing construction in the southern parts of the county has been much reduced from the pace of the 1960s, when more land was available. He added that, as children moved away from home, these communities are growing older and the households smaller.

Baltimore County, which rings Baltimore from the Dundalk area in the east to Brooklyn Park at the city's southern edge, showed similar trends, although the precise figures were not yet available, according to one county planner.

The county's own figures, which planner Kurt Kugelberg said will be reflected in the preliminary federal data show the working-class suburb of Dundalk losing population, while areas further to the west such as Randallstown and Owings Mills are continuing to grow.

Further south in Anne Arundel, the bulk of the country's growth took place along the major highways like Rtes. 2 and 3, in suburbs like Crofton and Arnold. But, while the city of Annapolis lost 1,500 people, according to the census bureau, thousands more found permanent homes along the inlets of the Severn and South Rivers, substantially increasing the population of the waterfront areas.

On the Eastern Shore, no county that had figures available registered large increases. Caroline County, which abuts Delaware, gained 2,000 people for a 6.6 percent increase, while Kent County, just northwest, gained 500 people and Talbot County, just southwest, gained 700.

No figures were available for Queen Anne's County, immediately across the Bay Bridge, or Worcester County, the home of Ocean City.

The figures that census officials sent to local planners for review, will be returned with comments or proposed corrections within the next month. Final statewide figures must be sent to the president by Jan. 1 1981. m