Outside political groups have poured more money into Virginia's U.S. Senate race than any other contest in the country except the presidential campaign as they battle over who will control the Senate next year.

A slew of political action committees, advocacy groups and party fundraising groups on both sides have spent nearly $24 million to influence the outcome of the race between Republican George Allen and Democrat Tim Kaine, according to the Center for Responsive Politics, a nonpartisan, campaign-finance watchdog group.

Most of the money paid for television attack ads against either Kaine or Allen, two former governors deadlocked over a seat that could determine whether Republicans or Democrats are running the Senate next year.

Top outside groups spending in Va. Senate race
1. Crossroads GPS $6,577,005
2. Majority PAC $4,392,580
3. U.S. Chamber of Commerce $2,675,717
4. Democratic Senatorial Campaign Committee $2,367,431
5. League of Conservation Voters $1,500,668
6. National Republican Senatorial Committee $1,499,846
7. AFSCME union $1,241,166
8. Service Employees International Union $962,683
9. Independence Virginia PAC $743,444
10. American Crossroads $728,653
Source: Virginia Public Access Project

Outside spending in the Virginia race is already nearly double the $13.6 million spent by similar groups in 2006 when Allen tried unsuccessfully to defend the seat against Democrat Jim Webb.

For months, Allen's campaign was the biggest beneficiary of the influx of outside cash. Pro-Kaine groups have since increased their activity and the money now is almost evenly split between Republican and Democratic groups.

Crossroads GPS, a group run by Republican strategist Karl Rove, former adviser to President George W. Bush, has pumped $6.5 million into Virginia, more than any other group, according to the Virginia Public Access Project. Majority PAC, an arm of Senate Democrats, is in second, having spent $4.4 million so far.

One of the latest outside groups to join the Virginia race is a pro-Allen Super-PAC called Independence Virginia, which is backed by Texas homebuilder Bob Perry, who helped underwrite Swift Boat Veterans for Truth, a group credited with influencing the outcome of the 2004 presidential race with its attacks on Democrat John Kerry. Perry has given $1 million to the Virginia PAC so far.

Independence Virginia also received $10,000 from Foster Friess, chief financial backer of Republican presidential candidate Rick Santorum's Super-PAC. Friess was widely criticized, and later apologized, for making a joke about contraceptives on the campaign trail.

Kaine tried to turn Freiss' support against Allen, calling Friess' views "intolerant."

"We should all agree that out-of-state contributions from individuals like Foster Friess should have no influence in this race," Kaine said.

Kaine in December called on Allen to denounce the use of outside money in the race, but Allen declined. By Monday, Kaine's campaign was promoting an ad put out by the Democratic Senatorial Campaign Committee charging that Allen's economic plan would eliminate 700,000 jobs.

The Allen campaign criticized Kaine for publicly denouncing outside spending while benefiting from it.

"It's pretty hypocritical for Tim Kaine to launch attacks on outside spending when labor unions, radical environmentalists and Washington Democrats are bankrolling his message," Allen spokeswoman Emily Davis said.

The two candidates are proven prolific fundraisers themselves. In one of the nation's most expensive races, Kaine has outraised Allen $15 million to $11.5 million.