RICHMOND -- Democrats seized control of the state Senate in Tuesday's General Assembly elections, creating a politically divided legislature that could give Gov. Tim Kaine greater leverage in the second half of his term.

Democrats won at least 21 of the 40 seats in the Senate, with one Northern Virginia race remaining too close to call late Tuesday night.

"It was a good night for my troops," said state Democratic Party Chairman Richard Cranwell of Vinton, after confirming that his party would win control of the Senate and end a decade of Republican rule in the chamber.

Republicans kept their majority in the House of Delegates, but Democrats cut into the GOP's majority by picking up four seats. Republicans won a Richmond-area House seat that had been held by an independent.

The power shift in the Senate is a victory for Kaine, who made an aggressive push to help Democrats throughout the state. The governor stumped for candidates and steered money from his political action committee to competitive races. He urged voters to send him more legislative allies to help pursue his agenda, which includes a targeted expansion of pre-kindergarten education.

Cranwell, a former House majority leader, said voters sent lawmakers a message that they want government to function "in a timely fashion and in a responsible fashion and they expect you to work together."

Kaine could face the task of working with a Senate controlled by Democrats and a House controlled by Republicans, many of whom have reservations about his pre-kindergarten initiative and his plan to tap the state's "rainy day" reserve fund to balance the current two-year budget. Lawmakers also must pass a new two-year budget in the upcoming legislative session, and respond to demands for mental health reforms that stem from the Virginia Tech shootings.

Republicans entered the campaign with a 23-17 majority in the Senate. Democratic challengers defeated GOP incumbents Nick Rerras of Norfolk, Jeannemarie Devolites Davis of Fairfax County and Jay O'Brien of Fairfax County. Democrats also won an open seat on the Peninsula that had been held by Republican Marty Williams, who was ousted in a June primary.

"Tonight's election results were clearly not what those of us on the Republican side of the aisle desired," said Senate Majority Leader Walter Stosch, R-Henrico County. "Still, we will persevere with renewed dedication in making positive contributions to the governing of the commonwealth."

Republicans held their own in three other closely watched races, including the 22nd District contest won by Republican Ralph Smith of Botetourt County. Some Democrats expected greater Senate gains heading into Tuesday's races.

"We had hoped to do better," said Sen. John Edwards, D-Roanoke, as returns came in Tuesday night. "All the polls indicated we would do better."

The results could affect Kaine's chances of winning support for a targeted expansion of pre-kindergarten education, which the governor has identified as a top priority for the second half of his term. Republican leaders have not embraced the proposal. They also have criticized Kaine for wanting to tap the state's "rainy day" reserve fund to address part of a $641 million budget shortfall.

Democrats entered the election with 40 House seats and gained at least two by winning Republican-held seats in Virginia Beach. Democratic candidates also held slight leads in two Northern Virginia districts where Republican incumbents have retired. But Republicans maintained control of the chamber, despite efforts by Democrats to hold the GOP responsible for passing new, controversial "abusive driver" fees earlier this year.

While Democrats tried to cast their Republican rivals as obstructionists, GOP leaders took credit for gains Virginia made during the eight years the party has controlled both houses of the legislature. Republicans also vowed to take the lead in cracking down on illegal immigrants, seizing on an issue that has galvanized communities in the Northern Virginia suburbs.

House Majority Leader Morgan Griffith, R-Salem, expressed disappointment over the loss of the Hampton Roads seats, but was satisfied with his party's efforts in Western Virginia. Griffith said it's too early to tell how the campaign will affect the relationship between Kaine and Republican lawmakers.

"There are going to be some hurt relationships based on how active the governor was," Griffith said.

House Minority Leader Ward Armstrong, D-Henry County, said the Democratic pickups will give the party greater leverage in the chamber. And, he added, I think we put ourselves in position to get the majority in 2009."

Democrats now have 44 seats in the House, while Republicans have 54.

"Clearly, the more seats we pick up and the closer we get, the more our side of any particular issue gets heard," Armstrong said.