GRESHAM, Ore. — Hours before being greeted by the biggest crowd of his campaign, Democrat Barack Obama told a small group of seniors yesterday that Republican John McCain would threaten the Social Security they depend on because he supports privatizing the program.

Fire officials estimated 65,000 packed into a riverside park for an afternoon rally on the banks of the Willamette River in Portland. They said an additional 15,000 were left outside and dozens of boaters could be seen floating on the river.

"Wow, wow, wow," Obama said as he surveyed the audience. "We have had a lot of rallies. This is the most spectacular setting, the most spectacular crowd we have had this entire campaign."

Obama's appearance early in the day before about 130 people at an assisted living facility to talk Social Security was an attempt to tie the GOP's presidential nominee-in-waiting to the unpopular President Bush on a pocketbook issue that motivates seniors — and also concerns younger generations worried about their own retirement.

"Let me be clear, privatizing Social Security was a bad idea when George W. Bush proposed it, it's a bad idea today," Obama said. "That's why I stood up against this plan in the Senate and that's why I won't stand for it as president."

Bush proposed a Social Security plan in 2005 that focused on creating private accounts for younger workers, but it never came up for a vote in Congress. Democrats opposed the idea and few Republicans embraced it.

Obama said McCain would push to raise the retirement age for collecting Social Security benefits or trim annual cost-of-living increases. Obama has rejected both ideas as solutions to the funding crisis projected for Social Security in favor of making higher-income workers pay more into the system.

"We have to protect Social Security for future generations without pushing the burden onto seniors who have earned the right to retire in dignity," he said.

McCain spokesman Tucker Bounds accused Obama of making "misinformed partisan attacks."

"John McCain has been clear about his belief that we must fix Social Security for future generations and keep our promises to today's retirees, but raising taxes should not be the answer to every problem," Bounds said.

It was a day of coastal campaigning for the two Democrats still competing for the party's presidential nomination.

Obama was in Oregon, where he is favored to win the state's presidential primary tomorrow. Hillary Rodham Clinton spent a second straight day in Kentucky, where she is favored to win when its voters head to the polls the same day.

She attended worship services at a Methodist church in Bowling Green, and happily sang hymns and joined in Bible readings. But her smile faded when the pastor launched into a sermon about adultery, asking his congregants whether the devil had ever whispered over their shoulders in their marriages.

Her mood appeared to brighten by the time she arrived for a rally at Western Kentucky University.

"Now, my opponent said the other day he wasn't coming back, so I've got the whole state to myself," Clinton said. "What a treat."