WESTERVILLE, Ohio -- Clinton campaign officials have accused Democratic rival Barack Obama of making a 'flub' during an Ohio speech in which he described the Iraq war vote cast by a leading senator who endorsed him.

Obama criticized Clinton expressly for failing to read the classified National Intelligence Estimate on Iraq's weapons capabilities, a report available at the time of her October 2002 vote authorizing the Iraq war.

He said that Sen. Jay Rockefeller, a fellow Democrat from neighboring West Virginia, had read the intelligence estimate as a member of the Senate Intelligence Committee and after a brief pause said the then-chairman had voted against the war resolution.

However, Rockefeller was not the chair at the time and voted in favor of the war authorization. Sen. Bob Graham of Florida was the intelligence committee chair in 2002 and voted against the resolution. Obama did not mention Graham's name in the passage.

"She didn't read the National Intelligence Estimates. Jay Rockefeller read it. But she didn't read it. I don't know what all that experience got her because I have enough experience to know that if you have a National Intelligence Estimate and the chairman of the national, um, Senate Intelligence Committee says you should read this, this is why I'm voting against the war, that you should probably read it. I don't know how much experience you need for that."

Clinton campaign spokesman Phil Singer said in a statement to FOX News, "Sen. Obama is so desperate to divert attention from his limited national security experience that he's not just misleading voters about Sen. Clinton, he's also misleading voters about his own supporters. That is not change you can believe in."

Obama's campaign countered that the Illinois senator was clearly referring to Graham in the reference to the intelligence chair who voted against the authorization.

"Apparently, the Clinton campaign read Senator Obama's remarks about as carefully as Senator Clinton read the National Intelligence Estimate, " Obama campaign spokesman Bill Burton said in a statement to FOX News. "Because the truth is the Chairman of the Senate Intelligence Committee in 2002 was Bob Graham, and he read the NIE, voted against the war, and counseled other Democrats to read the NIE before they voted -- Senator Clinton made a different judgment and gave George Bush a blank check for war."

Obama has stepped up efforts to fend off intensified attacks on his foreign policy credentials from rival Hillary Rodham Clinton on Sunday ahead of a potentially race-ending showdown in Ohio and Texas.

"What precise foreign-policy experience is she claiming that makes her qualified to answer that telephone call at 3 a.m. in the morning?" Obama asked of the former first lady at a town-hall meeting. It was a reference to dueling television ads over who would exercise superior judgment in responding to a national emergency in the middle of the night.

"When it came time to make the most important foreign policy decision of our generation the decision to invade Iraq Senator Clinton got it wrong," Obama said.

Rockefeller, who is now chairman of the committee, endorsed Obama on Friday and campaigned with him on Saturday.

Rockefeller called Obama "brilliant" and "well-grounded" and prepared to take the reins as commander-in-chief.

The Illinois senator also sought to ease lingering Internet-fed concerns about his religion, in particular whether he was a closet Muslim.

"I am a devout Christian. I have been a member of the same church for 20 years. I pray to Jesus every night," he declared at an earlier appearance in the rural southern Ohio town of Nelsonville. He said he wanted to halt "confusion that has been deliberately perpetrated."

Unlike Clinton, who has been barnstorming Ohio, Obama had only two events in the state on Sunday and was spending the night in hometown Chicago. He heads to Texas on Monday for a final day of campaigning before awaiting returns on Tuesday in San Antonio.

His aides said privately that they felt they had a good shot at a win in Texas, but were less certain about Ohio, where they braced for a possible loss.

The two senators came close to running into each other in this Columbus suburb, where Clinton spoke at one high school and Obama spoke several hours later at another. Obama supporters boasted of a much larger crowd.

Obama said his opposition to the war in 2002 was not a single speech -- as Clinton has asserted -- but a series of remarks during his 2002 successful Senate campaign.

The Obama campaign also lined up a conference call for reporters with various Democratic foreign-policy experts who asserted his ability to inspire and lead, his good judgment on Iraq, and ticked legislative accomplishments. It was an effort to undercut Clinton's claim that Obama foreign-policy experience was shallow.

In addition to foreign policy, Obama talked about economic issues affecting economically depressed Ohio, as had Clinton.

Recent polls show Clinton retains a lead in Ohio, although it has been narrowing. In Texas, her once formidable lead has all but vanished and the race is now seen as a dead heat.

Most Democratic strategists see Texas and Ohio as must-win states if Clinton is to continue her candidacy, a view also expressed by her husband, former President Bill Clinton.

She has lost 11 consecutive contests to Obama and lags in the delete count.

But in recent days, Clinton campaign officials have suggested that if Obama doesn't win all four Tuesday contests -- which also include races in Rhode Island and Vermont -- it would signal "buyers remorse" and be reason to continue the campaign to the next major primary, Pennsylvania on April 22.

FOX News' Major Garrett and Steve Brown and the Associated Press contributed to this article.