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Democrat Barack Obama said Thursday he was forgoing more than 80 million dollars in public financing for his White House campaign, leaving him free to tap unlimited private cash against John McCain.
   
"We've made the decision not to participate in the public-financing system for the general election," Obama said in a video message to his supporters.
   
The Democrat had pledged last year to work "aggressively" with the Republicans on a deal to preserve public financing, under which candidates limit their spending in return for matching funds from the federal Treasury.
   
"It's not an easy decision, and especially because I support a robust system of public financing of elections," said the Illinois senator, who becomes the first presidential candidate to forgo Treasury money for the general election.
   
But Obama said the finance system was "broken" and that every resource was needed to beat the Republicans in November's election.
   
"This means we'll be forgoing more than 80 million dollars in public funds during the final months of this election."
   
Obama has raised a stunning 265.4 million dollars so far in his bid for the presidency, smashing all records for this stage of the race, fueled by more than 1.5 million small donors who have given repeatedly over the Internet.
   
The Illinois senator said his online operation has become a grassroots alternative to the Washington system of financing, under which presidential candidates taking public money are limited to spending about 85 million dollars during the general election season.
   
McCain, who badly lags Obama in fundraising and says he is likely to take Treasury money, has accused Obama of breaking his "word" to voters over public financing.
   
The Democrat says he never made such a pledge, merely promising last year to consider the public limits in cooperation with the Republicans.
   
And in his video message, he said the stakes were too high to let the Democrats be hampered this year.
   
"John McCain's campaign and the Republican National Committee (RNC) are fueled by contributions from Washington lobbyists and special interest PACs (political action committees)," he said.
   
"And we've already seen that he's not going to stop the smears and attacks from his allies running so-called 527 groups, who will spend millions and millions of dollars in unlimited donations."
   
So-called 527 organizations, named after the section of the US tax code governing their activities, are political pressure groups that are meant to be unaffiliated with a candidate.
   
"From the very beginning of this campaign, I have asked my supporters to avoid that kind of unregulated activity and join us in building a new kind of politics -- and you have," Obama said.
   
"This is our moment and our country is depending on us," he said, listing the Iraq war, healthcare, education and the economy as defining issues for November's election.
   
"So join me, and declare your independence from this broken system and let's build the first general election campaign that's truly funded by the American people."
   
Lawyers for the two campaigns met in the past fortnight to discuss public financing "and it was immediately clear that McCain's campaign had no interest in the possibility of an agreement," Obama spokesman Bill Burton said.
   
"When asked about the RNC's months of raising and spending for the general election, McCain's campaign could only offer its expectation that the Obama campaign would probably, sooner or later, catch up," he told AFP.
   
"And shortly thereafter, Senator McCain signaled to the 527s that they were free to run wild, without objection."
   
There was no immediate comment from the McCain campaign.