By Alina Selyukh and Alexander Cohen
WASHINGTON (Reuters) - Two groups formed by influential Republican operative Karl Rove spent more on television and radio ads in the presidential race than any other "super PAC" or advocacy group in recent weeks, blanketing airwaves in advance of the November 6 election.
The super political action committee American Crossroads and its sister nonprofit, Crossroads GPS, together spent $47.4 million since September 10, according to Reuters analysis of spending disclosures filed with the Federal Election Commission through October 18.
Ads funded by the groups, which have pledged to spend some $300 million to help elect Mitt Romney to the White House and Republicans to Congress, have been hitting President Barack Obama's economic record in a handful of crucial swing states.
"October is when the rubber hits the road," said Crossroads spokesman Jonathan Collegio. "Our pedal is on the metal and will continue to be on presidential and congressional advocacy."
Rove is an often-controversial Republican strategist. He was the architect of George W. Bush's two successful presidential campaigns and lately has leveraged his influence and connections to help Romney and fellow Republicans through the formidable Crossroads duo.
Spending from all sources in the Obama-Romney race so far makes it the most expensive U.S. campaign.
Since September 10 alone, nearly 50 active outside groups have already spent $108.6 million on television, cable and radio in the presidential race, according to Reuters calculations.
Democrats have spent much of 2012 decrying Republican outside spending groups, like American Crossroads and Crossroads GPS, a tax-exempt advocacy group that does not disclose donors.
But the pro-Obama super PAC Priorities USA Action has lately overtaken many of its Republican rivals as Democrats overcome their resistance to the idea of super PAC spending, which often is funded by small groups of wealthy businessmen.
Since early September, Priorities has become the second-biggest spender of the campaign season, running $18.6 million worth of ads, many of which paint Romney's economic policy plans as anti-middle class.
Restore Our Future, Romney's formidable helper during his fight for party nomination against other Republicans, slowed its ad onslaught, reporting $9.7 million spent in the past five weeks, according to the group's FEC filings.
Both Super PACs and tax-exempt groups are allowed to raise unlimited cash as long as they do not coordinate efforts with campaigns or national parties. Super PACs have to disclose their donors, while non-profits, trade groups and other tax-exempt organizations can keep their financiers secret.
FLURRY OF REPUBLICAN GROUPS
Notably absent from the top spenders list is the powerful conservative group Americans for Prosperity, funded by billionaire brothers David and Charles Koch.
After heavy on-air presence for most of the year, the advocacy group in early September shifted its focus from the TV air war almost entirely onto its grassroots work and this week launched a direct mail campaign. Its first $2 million kick-off focused on federal debt and is expected to reach some 4 million Americans, said spokesman Levi Russell.
"Campaigns and other groups are absolutely beating airwaves to death," Russell said. "It makes more sense for us to leverage our activists, our boots on the ground ... rather than TV ads."
The rise and success of Republican groups in the 2010 congressional elections and millionaire Romney's appeal to higher-income Republicans had led most campaign finance experts to predict that Democrats would get all but squeezed out from television screens in the run-up to the November 6 vote.
However, ads by Obama's re-election campaign - fed partially by big checks but notably by smaller grassroots donations - have largely kept up the biggest presence on the airwaves so far this campaign season.
Republican super PACs and tax-exempt groups as have helped Romney close the gap with Obama as the candidate himself did not become the official nominee or start his anti-Obama campaign in earnest until late August.
The third biggest Republican spender since the party conventions kicked off the general election cycle is Americans for Job Security, a conservative tax-exempt organization. It has reported spending $8.2 million on ads since September 10.
Other big spenders were the Republican Jewish Coalition, which has reported investing $4.5 million in ads, and American Future Fund, another conservative tax-exempt group, has spent $3.7 million on anti-Obama ads.
(Editing by Bill Trott)