AFP boasts chapters in 34 states and its field operations have included annual conservative conferences.
Phillips cited Florida, where the group now has a staff of 20 and has promoted bus tours assailing Obama and Democratic Sen. Ben Nelson.
"We use our rallies to let people know how their president and their senators and congressmen are voting on key issues," Phillips said. "A rally focusing on government over-spending can be as effective as a media buy."
The Romney campaign, by contrast, has not run its own TV ads since former Pennsylvania Sen. Rick Santorum dropped out of the GOP nomination fight in April.
Senior Romney aides said they are closely tracking the super PAC ad buys from allies but insist there is no coordination between the campaign and the outside groups.
At the same time, Romney's team also is working to improve relations with Sheldon Adelson and Foster Friess, billionaires who almost single-handedly financed super PACs supporting Romney's opponents during the nomination fight.
Representatives of ROF and other Romney backers have reached out to Adelson, a casino mogul who contributed about $20 million to a super PAC supporting Newt Gingrich. But Adelson has not yet given money to the pro-Romney efforts, and a person close to him said he doesn't want to be a campaign distraction and may give money only to groups like Crossroads GPS and other nonprofit advocacy organizations not required to disclose their donors.
Friess, who helped bankroll a super PAC supporting Santorum, has said he would back Romney and has spoken to Romney supporters.
Romney's campaign concedes that the super PAC activity alleviates financial stress as he works to add staff and raise campaign cash.
His aides are also noting Priorities USA Action's slow start compared to the pro-Romney groups. The disparity is fueling a quiet confidence among Romney advisers who believe that his super PAC support will significantly narrow Obama's current 10-to-1 cash advantage.
Associated Press Writers Jack Gillum, Steve Peoples and Stephen Braun in Washington contributed to this report.
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