PAOLI, Pa. -- Sen. Barack Obama indicated yesterday he might renege on a campaign spending agreement if spending by third-party committees isn't limited, too.

Both Mr. Obama and presumptive Republican nominee John McCain had previously told the Federal Elections Commission they would accept $85 million in public money instead of raising private dollars to finance their general election campaigns.

Now that Mr. Obama has raised more than $193 million to Mr. McCain's $66 million, he says he will follow through on that pledge only if there are assurances that political action committees and others follow the spirit of the agreement, too.

He pointed to the Swift Boat Veterans for Truth's involvement in the 2000 election. The group ran commercials attacking Sen. John F. Kerry, and its leaders donated millions to President Bush's campaign.

"I don't want Democrats to heavily disarm if we can't create a system where outside parties and third parties run Swift Boat ads, outspending the Democratic nominee," Mr. Obama said as the train made its way from Wynnewood to Paoli. "That's not something I would agree to. I want to make sure everybody plays by the same rules."

He insisted he has not changed his position.

"What I said very early on is that I would sit down with my Republican opponent and try to find a way to preserve public financing. I was the one who asked whether this was an option," he said. "If it wasn't for my queries to the FEC it wouldn't even be an option for anyone."