WASHINGTON -- Hillary Rodham Clinton had the Democratic presidential campaign trail to herself, but the camp of vacationing rival Barack Obama challenged the former first lady on her claim to have landed in Bosnia 12 years ago under sniper fire.

Clinton characterized the episode as a "misstatement" and a "minor blip." Obama spokesman Tommy Vietor said in a written statement Monday that her story "joins a growing list of instances in which Senator Clinton has exaggerated her role in foreign and domestic policy-making."

Clinton spokesman Howard Wolfson countered that the Obama campaign was only raising the issue because "they have nothing positive to say about their candidate."

Obama's campaign machinery refused to allow the former first lady's Bosnia story pass without getting in a dig.

During a speech about Iraq last Monday, she said of the March 1996 Bosnia trip: "I remember landing under sniper fire. There was supposed to be some kind of a greeting ceremony at the airport, but instead we just ran with our heads down to get into the vehicles to get to our base."

According to an AP story at the time, Clinton was placed under no extraordinary risks on that trip. One of her companions, the comedian Sinbad, told The Washington Post he had no recollection either of the threat or reality of gunfire.

The Obama campaign statement carried Internet links to a CBS news video taken from the Bosnia trip and posted on YouTube. It showed Clinton and her daughter, Chelsea, walking across the tarmac from a large cargo plane, smiling and waving, and stopping to shake hands with Bosnia's acting president and greet an 8-year-old girl.

When asked Monday about the New York senator's recounting of those events, Wolfson recalled Clinton's book, "Living History," in which she described a shortened welcoming ceremony at Tuzla Air Base, Bosnia-Herzegovina.

"Due to reports of snipers in the hills around the airstrip, we were forced to cut short an event on the tarmac with local children, though we did have time to meet them and their teachers and to learn how hard they had worked during the war to continue classes in any safe spot they could find," she wrote.

Wolfson said: "That is what she wrote in her book. That is what she has said many, many times and on one occasion she misspoke."

Asked about the issue during a meeting with the Philadelphia Daily News' editorial board on Monday, Clinton said she "misspoke."

"I went to 80 countries, you know. I gave contemporaneous accounts, I wrote about a lot of this in my book. You know, I think that, a minor blip, you know, if I said something that, you know, I say a lot of things -- millions of words a day -- so if I misspoke, that was just a misstatement," she said.

Clinton often cites the goodwill trip she took with her daughter and several celebrities as a part of her foreign policy experience, which she claims gives her an advantage over Obama.

Vietor questioned whether Clinton misspoke, saying her comments came in what appeared to be prepared remarks for the Iraq speech. His statement for the Obama campaign included a link to the speech on Clinton's campaign Web site with her account of running to the cars. Clinton's campaign said what is on the Web site is not the prepared text, but a transcript of her remarks, including comments before the speech in which she talked about the trip to Bosnia.

While Obama took time off in St. Thomas, the U.S. Virgin Islands, Clinton spoke to invited guests at the University of Pennsylvania in Philadelphia and called on the Bush administration to name an emergency working group on home mortgage foreclosures to find new ways to solve the U.S. housing crisis.

The campaign of Obama, who leads Clinton in pledged delegates, state primary contests won and popular vote, announced a six-day "Road to Change" bus tour across Pennsylvania, which holds the next presidential primary contest on April 22. The tour was to begin on Friday. Polls show Clinton with a substantial lead there.

The intense interest in the race has been reflected in a surge in Democratic Party enrollment past the 4 million mark setting a state record for either party, according to state election officials. Both the Obama and Clinton campaigns had been pushing to sign up new Democratic voters by Monday, the last day Pennsylvanians had to register to vote in the primary.

While Democratic enrollment was up by more than 4 percent, Republican enrollment declined by about 1 percent to 3.2 million statewide.