WASHINGTON — Anonymous donors behind shadowy “super PACs” that have shaped the 2012 Republican presidential race by funding a slew of attack ads, were finally to be exposed Tuesday, the deadline to release their financial reports.

The PACs, or political action committees, numbered a total of 302 groups as of January 31, according to the Federal Election Commission, and had spent a collective $44.9 million. They have so far been the work of unknown donors, working to back candidates by launching caustic attacks on their rivals.

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The groups have until midnight to file their records to the Federal Election Commission.

One of the most well-known players in the field revealed its records Monday — comedian Stephen Colbert’s group “Americans for a Better Tomorrow, Tomorrow,” aimed at skewering the entire finance-in-politics issue, revealed it had raised a whopping $1.02 million, mostly from multiple small donations.

A handful of the wealthy backers have been known, by name at least — US casino magnate Sheldon Adelson has reportedly donated some $10 million so far to the group backing Newt Gingrich called “Winning our Future,” blasting rival frontrunner Mitt Romney as weak choice for the Republican nomination.

A pro-Romney group, with a similarly upbeat name, “Restore Our Future,” has also been hitting airwaves in Florida ahead of the key primary election Tuesday, using millions in anonymous donor cash to slam Gingrich, reminding voters of what they say are his past ethical and moral failings.

The Romney-backing PAC has spent some $8 million to air over 13,500 spots on his behalf in media markets in Iowa, South Carolina, Florida, Arizona and Michigan, according to a study conducted by Wesleyan Media Project.

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The super PACS, following recent Supreme Court rulings, can raise and spend unlimited funds without being subject to the same limits imposed on individual candidates.

Their influence has boomed this cycle compared to the 2008 election, with a more than 1,600 percent increase in interest group sponsored ads.

Their influence has been credited in shifting momentum in states that have voted so far, even more so than the candidates’ efforts in debates and slogging away on the campaign trail.

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“One reason we’ve seen the Florida polls shift in Romney?s favor over the past few days, when the national polls have not, is that his message has dominated the paid airwaves,” said Wesleyan Media Project director Travis Ridout.

Rivals Gingrich, former senator Rick Santorum and congressman Ron Paul “have had a much more difficult time making themselves heard” over the Romney campaign, said Ridout.

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The top candidates Romney and Gingrich have denounced the attacks launched by each other’s anonymous super PACs, calling them to stop the negative campaign.

Romney-backing “Restore Our Future” is at the top of the list, having raised $12,231,700 so far this cycle, according to data posted on the Center for Response Politics group OpenSecrets.orgwebsite.

Far behind is “Endorse Liberty” which supports Paul, spending just over $3 million so far, and the Santorum supporting group “Red, White and Blue,” with just under $2 million in expenditures.

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Colbert, as he filed his financial records to the FEC, made a sarcastic swipe at the process by pointing out voters in states that have already weighed in the Republican race could have benefited from the information before casting their ballots.

“It’s a great day for transparency because tomorrow voters in Iowa, New Hampshire, South Carolina, and Florida will finally have the vital information that would have been useful before they voted,” said the star of the eponymous Colbert Report show on Comedy Central.