Voters go to the polls throughout Virginia on Tuesday to decide dozens of legislative races that together will determine control of the General Assembly and the shape of state political power for at least the next decade.

After years of steady gains, Republicans believe they are on the verge of taking control of the General Assembly for the first time in more than a century. If they pick up just a single House of Delegates seat and maintain their edge in the state Senate, Republicans will control every part of state government, from the governorship on down.

They also will have unchallenged authority over redrawing state and federal legislative districts, a tool that could tip the balance of elections for the next 10 years and even affect the makeup of Congress.

The stakes have brought a historic flood of spending from both parties, big business givers and other interest groups. But strategists from both sides say the elections will turn on who shows up to vote Tuesday on races that are quintessentially local, more resembling elections for a small-town mayor than governor.

Quick impressions of candidates at civic association meetings or on doorsteps can have as much effect as glossy campaign literature. And in Northern Virginia, few candidates can afford to buy time on local television, making it harder for voters to tune in.

Several of Virginia's most hotly contested races are in the Washington suburbs. Democrats are pegging their chances for making gains in the state Senate on former congresswoman Leslie L. Byrne's challenge of Sen. Jane H. Woods (R) in Fairfax. And yet the support for an independent, conservative Virginia T. Dobey, could swing that race.

Republicans, who now share power in the House of Delegates, look to gain an edge in Thomas M. Bolvin's challenge of veteran Democratic Del. Gladys B. Keating in southern Fairfax. And in the same area, Republicans Scott T. Klein and Daniel F. Rinzel are campaigning to claim open seats long held by Democrats. Several western Fairfax incumbents are facing tough challengers this year as well.

In Prince William County, rookie Del. Michele B. McQuigg (R) is a top Democratic target. And in Loudoun County, Democrats are taking a shot at Del. Richard H. Black (R), another rookie, who has emerged as one of the General Assembly's most conservative members on social issues.

A swing toward either party in these and a handful of other races could easily determine control of the General Assembly as major debates loom on health care reform, education, transportation and efforts to battle illegal drugs.

There are broad areas of agreement between both parties on some of these issues. Democrats and Republicans both back $2 billion or more in new spending on transportation, with much of the money coming from Virginia's share of the national tobacco settlement.

Candidates from both parties also call public education a top priority and vow to devote more state money to building schools, hiring teachers and shrinking class sizes. There is also broad support for the Standards of Learning tests now used to measure the progress of students and their schools, though candidates from both parties agree that the tests need to be improved.

But each of these issues, and several others such as gun control and growth management, are cast differently in the contested races throughout the region.

It will be the accumulation of results in these individual races that will hand the Republicans a historic takeover of the General Assembly or allow the Democrats to hang onto power and perhaps even add to their ranks.

The state Senate is now split 21-19 in favor of the Republicans. In the House of Delegates, there are 50 Democrats, 49 Republicans and one independent who usually votes with the Republicans. All 140 seats are up for election.

Democrats warn that a Republican takeover would embolden Gov. James S. Gilmore III (R) to pursue a more conservative agenda on social issues such as abortion, end-of-life decisions and school vouchers. Gilmore and the Republicans have said little on these issues during the campaign, but Craig Bieber, executive director of the state Democratic Party, said a Republican majority will mean gains for "the right-wing social agenda."

"It really is the right-wing tail that wags the Republican dog," Bieber said. "That stuff is going to come up if the Republicans take over."

Republicans call that nothing more than Democratic scare tactics. They say a GOP majority would allow Gilmore to build on recent accomplishments on tax relief, sending lottery money to public schools and cutting the price of higher education. Internet issues have also topped Gilmore's agenda and are likely to remain prominent as Northern Virginia's high technology community grows.

"Because they don't have any great policies, they have to bring out the boogeyman every year," says Ed Matricardi, political director of the state Republican Party. "I don't think anyone has anything to fear from Governor Gilmore."