Conservative activists nationwide are mounting an aggressive voter mobilization effort and building an extensive field organization network designed to provide Republican nominee Mitt Romney and other GOP candidates an edge if the race is close.

Both the organizers of the efforts and some worried Democratic strategists say they are already seeing results.

President Obama's campaign has focused much of its effort on mobilizing its celebrated grass-roots network of expert organizers and neighborhood team captains. But in key battleground states, that machinery is being challenged by a conservative coalition that includes the National Rifle Association, billionaire-backed Americans for Prosperity and a newly muscular College Republicans organization with a $16 million budget. The conservative groups "are fully funded and ready for hand-to-hand combat," said Steve Rosenthal, a longtime Democratic organizer.

Rosenthal is the co-founder of the Atlas Project, a group tracking voter statistics to help guide Democratic groups as they design precinct-level voter-outreach strategies. In reviewing data in recent weeks, he has grown alarmed at what he views as a successful, years-long campaign on the right that could alter the electoral landscape.

In Florida, for example, Republican legislation, since overturned in the courts, effectively dampened pro-Democratic voter registration efforts during critical months in 2011 and 2012, resulting in registration gains for Republicans in the crucial Tampa Bay area since Election Day 2008.

In Ohio, the evangelical group behind a successful anti-gay marriage amendment that helped mobilize conservative voters in 2004 claims it now has a network of 10,000 churches and a database of millions of rural voters who will be targeted with in-person visits and voter guides.

And in Wisconsin, a traditionally Democratic state, conservatives have built a house-by-house turnout machine already tested in the successful campaign to repel a union-backed recall of GOP Gov. Scott Walker in June.

On the ground, the battle remains close and hard-fought. Experts say that if Obama's lead in key states extends beyond a few points, even the most effective field operation on the right may not be enough to prevent a Romney loss. But, they say, the operation can add two to three points to Romney's total and, in a close contest, that could be a significant difference.

One of the major players on the right is Americans for Prosperity, the group co-founded by billionaire David Koch. The group plans to spend $125 million on the 2012 campaign, half of it devoted to field organizing in political battlegrounds. AFP has 116 staff members on the ground targeting 9 million voters that the group has found to be "up in the air" about how to assess Obama's economic record, said its president, Tim Phillips.

"This is a totally new ballgame," said Luke Hilgemann, the Wisconsin director for AFP, who oversees 12 full-time staff members and thousands of volunteers. "We're matching the left and exceeding them in lots of things that we're doing."

Obama aides insist that the president's grass-roots network will be more effective, though they acknowledge the landscape has changed. "It's a much more robust field operation than the 2008 McCain campaign had, that's clear," said Jim Messina, Obama's campaign manager. But, he added: "The other side is trying to pay to replicate what we spent years to build."