Newly released census figures promise increased political clout for the growing Washington suburbs, but set the stage for controversy over whether majority black congressional districts will be created in Virginia and Maryland.

Census figures are the basis for the once-a-decade redrawing by state legislatures of election districts, from school board to congressional, which must have approximately equal numbers of voters. Census numbers also determine some federal aid, which can be a cornerstone of city budgets but which makes up less than 5 percent of suburban spending.

Preliminary population counts were issued late last month. The Census Bureau will weigh challenges from jurisdictions that claim their populations actually are larger, and final figures will come out by early next year.

But the preliminary figures suggest that the Northern Virginia suburbs will add three delegates to the 21 they now have in the 100-member state House, and the equivalent of a senator and one-half to the region's eight now in the 40-member state Senate.

That would give the area, credited with one-third of Virginia's total population growth since 1980, a full 25 percent of the seats in the General Assembly, boosting the local caucus at a time when Tidewater suburbs are growing and the rural southwest population is shrinking.

"The growth has shifted dramatically to the urban crescent," said state Sen. Joseph V. Gartlan (D-Fairfax), chairman of the Privileges and Elections Committee. "If the interests of those areas coincide, those interests are going to prevail."

Maryland's Montgomery County, which surpassed Baltimore and Prince George's County to become the state's largest jurisdiction, could acquire one new senator and three more delegates in the General Assembly. Baltimore may lose the same number.

"It will translate into a shift of power," said state Senate President Thomas V. Mike Miller Jr. (D-Prince George's). Even a single new senator can make a difference, he said, citing an abortion bill approved this year on a 24 to 23 vote.

According to preliminary estimates by Maryland's Planning Department, Prince George's County and Baltimore County each will lose part of a district even though they gained population, because other places grew faster. Howard County will gain half a district, and other suburban counties would get smaller fractions. Each district has three delegates and a senator.

The number of legislators from an area is only one factor in determining its political power, observers say. The Maryland suburbs have not built coalitions in Annapolis, and influence can hinge more on having a local lawmaker in a leadership job. "If people are expecting a sea change in priorities with reapportionment, they'll be disappointed," said one local legislator.

Across the Potomac River in Virginia, "the good news for Republicans is that the growth is in suburban areas," said Steve Haner, a spokesman for the state GOP, outnumbered by 11 in the state House and 10 in the Senate. "These are areas of natural strength."

Virginia's 14.6 percent population increase since 1980 -- up to 6.1 million -- apparently will bring the state an 11th congressional district. Northern Virginia Democrats want to add that seat in their area, carving a Democratic-leaning district to add to the two now represented by Republicans.

But black political leaders and voting rights groups are pressing instead for creation of the state's first black congressional district, in the Tidewater area. Tidewater grew in the 1980s, but not by as much as Northern Virginia.

Based on where the population is, the seat "should be in Northern Virginia," and that is "more than likely" where it will go, Gartlan said.

Frank R. Parker, voting rights project chairman of the Lawyers Committee for Civil Rights Under Law, said the federal Voting Rights Act and court rulings interpreting it require that if current voting in an area is racially divided and a new black district can be created, it should be.

"If a majority black congressional district can be created and the General Assembly fails to create one, then we'll sue," he said.

Parker's group was among several that sued over Virginia's last redistricting plan, which took two years to implement amid controversy. Virginia is one of 16 states that must have all or part of its redistricting plans approved for racial representation by the U.S. Justice Department under the Voting Rights Act.

Blacks have an unlikely ally in their campaign for congressional seats -- the Republican Party, which assumes that minority districts would vote Democratic but that surrounding districts would become more strongly Republican. The GOP has offered expensive computer help to voting rights groups.

In Maryland, black leaders are pushing for a mostly minority congressional district in increasingly black Prince George's County, and the redistricting prompted by the new census numbers may help them realize their ambition. If no such district is created, they believe it could divide the Democratic Party, opening the door for Republican inroads.

"I fully expect some accommodation will be reached," said state Sen. Albert R. Wynn (D-Prince George's).

At the same time, Democrats are eager to protect Rep. Steny Hoyer (D-Md.), a white member of Congress in an increasingly black district. Hoyer is a Democratic Party power who needs to shore up his political base with additional white voters from other areas through redistricting.

Maryland's preliminary numbers -- a 12.2 percent increase to 4.7 million -- fall short of the numbers needed to create a new congressional district. Drawing new lines to protect Hoyer and accommodate black ambitions mean someone else loses out, either Republican Rep. Constance A. Morella to the northwest in Montgomery County, or conservative Democratic Rep. Roy P. Dyson to the south.

The Virginia General Assembly will hold a special session on redistricting in April, aiming to set new districts for next year's legislative elections and 1992 congressional voting, although challenges could delay that.

The Maryland General Assembly will meet in the fall of 1991 on congressional districts, anticipating the 1992 elections, and early in 1992 on legislative districts in preparation for 1994 elections.