WASHINGTON — Democrat Barack Obama's decision to walk away from more than $84 million in taxpayer money for the general election signals trouble for a system created to limit the influence of special interests, experts say.

Obama yesterday set aside an early promise to use public funds for the fall and became the first presidential nominee to bypass the system since it was created in 1976 after the Watergate scandal.

Republican John McCain will accept public funding for the fall campaign. He applied for the money for the primaries, but did not use it.

"We've known for some time that the public-financing system was on the verge of breaking," said Richard Hasen, a campaign-finance expert at Loyola Law School in Los Angeles. "Now that the first major party candidate has opted out of it, it shows that is broken."

Hasen and Anthony Corrado, who teaches at Colby College in Maine, note that campaign-finance laws limiting contributions and setting levels for public money have not kept pace with the high costs of TV advertising and other expenses for a White House bid.

"It's outdated and it's inadequate," Corrado said.

Obama's top campaign aides said the Illinois senator is forgoing taxpayer money because McCain has been raising general-election funds since March, when the Arizona senator clinched his party's nomination. Obama clinched on June 3.

In a video statement, Obama said his decision was prompted by the ability of party committees, outside groups and wealthy individuals to influence the election with their own spending.

"It was not an easy decision, especially because I support a robust system of public financing of elections," he said. "We face opponents who have become masters at gaming this broken system."

McCain, speaking from Iowa, said the fact that Obama was "not even willing to keep" a campaign promise "should be disturbing to all Americans."