June 29 (Bloomberg) -- John McCain, in his sharpest attack yet against rival Barack Obama, said the Democratic presidential candidate's word ``cannot be trusted.''

``This election is about trust -- trust in people's word,'' McCain, the presumptive Republican presidential nominee, told several hundred donors at a $2 million GOP fundraiser in Louisville, Kentucky, yesterday. ``And unfortunately, apparently on several items, Senator Obama's word cannot be trusted.''

McCain, a four-term Arizona senator, said Obama has gone back on his word by pledging to take public financing during the general election and then deciding not to do so. Obama on June 19 announced he won't accept public financing for his presidential campaign, calculating that he can raise far more than the $84.1 million he would get in government funds.

Obama's decision was a turnaround from a signed pledge to pursue an agreement with McCain to accept public funds and the spending limits that go with them. That was before Obama began hauling in record amounts of donations, and doing so would have meant surrendering a significant advantage over McCain. Negotiations between Obama and McCain never took place.

In recent days, McCain has rapped Obama for reversing his position on the matter. Still, until yesterday McCain hadn't accused Obama, 46, a first-term Illinois senator, of being untrustworthy.

Trust Me

``I'll keep my word to the American people. You can trust me,'' McCain said.

McCain's campaign in recent days has issued statements saying Obama has softened his stances on such issues as re- negotiating the North American Free Trade Agreement.

The Obama campaign, in turn, has said McCain has reversed himself on key matters, pointing to McCain's support for extending the Bush tax cuts after voting against them in 2001 and 2003. McCain this month also abandoned his support for a federal ban on offshore drilling for oil and natural gas, saying such decisions should be left to the states.

Responding to McCain's attack, Bill Burton, an Obama spokesman, said in an e-mail that ``Senator McCain's path to the nomination required repeatedly changing his positions to appeal to the Republican base.

``From supporting Bush tax breaks for the rich that he once voted against to saying he'd now vote against his own immigration reform legislation, the John McCain of 2008 is completely different from the man we knew just a few years ago,'' Burton's e-mail said.

Olympic Sport

Obama supporters are quick to highlight areas where McCain has changed his opinions in an attempt to label him as a worse ``flip-flopper'' than Obama. McCain has also changed his views on evangelical voters and offshore drilling, his supporters say.

``If flip-flop was an Olympic sport, John McCain would be the first to win a gold medal,'' Democratic Representative Rahm Emanuel of Illinois said today on ABC's ``This Week.''

The changes will end up hurting McCain's chances with independent-minded voters who want to see a change from the Bush administration, said Ed Rendell, the Democratic governor of Pennsylvania.

``John McCain has switched positions on all of the things that made independents and moderates and even some Democrats like myself think that he was a new type of Republican,'' Rendell said on the ``Fox News Sunday'' program. ``These are core issues.''

Financing the Election

Obama's decision makes him the first major-party candidate to opt out of the public financing structure for the general election campaign since the system was created after the Watergate scandals more than 30 years ago.

After Obama's declaration, McCain initially said he also would consider opting out, but hours later he said he would abide by his commitment to take taxpayer financing for his campaign.

McCain supporters point to Obama's decision to reject public financing as an example that he would not keep his word and is not serious about making substantial changes in government. Opting out of federal funding is a ``core issue,'' said Republican Rob Portman, former Ohio congressman and Bush administration budget director.

``It goes to more than just changes in facts and circumstances,'' Portman said on Fox. ``It goes to sort of changing your approach to politics.''

`Silly Season'

Jon Corzine, the Democratic governor of New Jersey, dismissed the criticism of Obama's decision not to take public funds.

``It's the silly season of campaigns, and so people use the `lie' word a little loosely,'' Corzine said on CNN's ``Late Edition'' program. ``And I think that is the case here as well.''

McCain today met with the Reverend Billy Graham and his son, the Reverend Franklin Graham, at the Graham family's mountain retreat outside Asheville, North Carolina. The senator said he thanked the elder Graham for having met twice with his parents and prayed with them for him while McCain was a prisoner in Vietnam.

McCain described today's 45-minute session as a private, non-political meeting and therefore he did not ask for their votes. In a statement released to reporters, Franklin Graham said he and his father were ``pleased'' to have met with McCain, who sought the meeting, and said he was ``impressed'' with McCain's personal faith.

Obama spent yesterday meeting with wounded troops at Washington's Walter Reed Army Medical Center and wooing government officials from the nation's growing Latino community in Washington at a meeting where McCain also spoke.

To contact the reporter on this story: Edwin Chen in Louisville, Kentucky at echen32@bloomberg.net.

Last Updated: June 29, 2008 16:48 EDT