John Edwards took another step forward in his attempt to take the "agent of change" mantle from rival Barack Obama and win over Iowa caucus-goers, declaring Saturday that special interest lobbyists would be banned from working in the White House if he is president.

"I'm proud of the fact that I have stood up against Washington lobbyists and special interest PACs, and I want to make an announcement today, which is when I am president of the United States, no corporate lobbyist or anyone who has lobbied for a foreign government will work in my White House," Edwards said in Washington, Iowa.  

The former North Carolina senator said Friday that those who take money from special interests cannot bring change to Washington, a criticism aimed at his leading rivals as they compete for undecided voters in Iowa's upcoming Jan. 3 caucuses.

Sens. Hillary Clinton and Obama have debated who is best suited to put the nation on a different track. Clinton contends that it takes experience more than desire, and Obama maintains that expecting change from the same Washington players is too much of a gamble.

But the race in Iowa is airtight, with Edwards seeing some last-minute momentum. A Strategic Vision poll taken Dec. 26-27 of 600 likely voters showed Obama with 30 percent, Clinton with 29 percent and Edwards with 28 percent.

Edwards' declaration Saturday may have been more of a shot at Obama, who after initially declaring that no lobbyist would work in his White House backpedaled to say no one who worked as a lobbyist would work on the same issue in his White House.

In veiled criticism of Obama, Edwards has said at recent events that if a candidate believes that he or she can sit down at the table and negotiate with special interests, then the candidate is living in "Never-Never Land" and that it's a "fantasy" to think that way.

Obama's campaign has responded to such criticism by saying that Edwards has advocated bringing special interests to the table for discussions.

"Early in this campaign, Barack Obama introduced the furthest-reaching lobbying reform proposal of any candidate in this race, and we appreciate that John Edwards is now following his lead in an attempt to distract attention from the fact that outside groups are exploiting campaign finance loopholes to spend millions of dollars to benefit his campaign," Obama spokesman Bill Burton said in a statement Saturday. "But the truth is, in his six years as a U.S. Senator, John Edwards did not propose or accomplish a single thing to reduce the power of lobbyists while Barack Obama passed the most sweeping lobbying reform since Watergate."

Obama's campaign has complained about big spending by outside groups friendly to Edwards, though Edwards insisted Saturday he has not taken any money from special interests.

"His campaign simply exploited the biggest loophole in the campaign finance system in order to get public matching funds while arranging through allies to benefit from a 527. That's how they avoided the spending limits that are a condition of the public matching funds," Obama campaign manager David Plouffe said in a statement.

His memo was prompted by disclosure of a $495,000 donation from philanthropist Rachel Mellon to a 527 group called the Alliance for a New America that is running ads in Iowa in support of Edwards' campaign. The nonprofit 527 groups can legally carry out some political activity but have come under scrutiny by the Federal Election Commission for their advertising during past presidential campaigns.

An FEC report showed the donation came from Oak Spring Farms LLC, the corporate entity that holds Mellon's fortune. Mellon is the 97-year-old widow of Paul Mellon, the son of industrialist Andrew Mellon.

She also contributed the maximum $4,600 allowed to Edwards' campaign earlier this year. The lawyer who serves as director of the investment fund, Oak Springs Farm LLC, also has contributed the maximum $4,600 allowed to Edwards' campaign.

Edwards dismissed the Obama camp's criticism of outside spending. Edwards, who often rails at special interests and greedy corporate America during his campaign stops, also jabbed at Clinton in Iowa. While he didn't mention Clinton by name, he criticized her for taking campaign contributions from special interests.

"To get real change, we need a president who will stand up against the big corporations and powerful interests who control Washington," he told about 250 people in Dubuque. "Nobody who takes their money and defends the broken system is going to bring change."

Edwards assured a crowd at a stop earlier in the day in Independence, Iowa, that he'll work diplomatically with fellow lawmakers and save his ire for the powerful interests.

"I'm not talking about fighting politicians. Nobody is interested in seeing a bunch of politicians fight," he said. "We're going to put the power in the people, and that's what this democracy is."

The Edwards campaign announced a new "Ask John" program that will give voters throughout Iowa a chance to ask him questions in the final days leading up to the Iowa contest.

Edwards promised that every person asking a question -- through a new Web site, a telephone bank and at campaign stops -- will get a response by caucus night on Thursday.

FOX News' Cristina Corbin, Bonney Kapp and Major Garrett and The Associated Press contributed to this report.