WASHINGTON – President Bush struck back yesterday at Democrats blaming him for the disappearance in Iraq of hundreds of tons of explosives. The response came as opinion polls showed a confused election map, with more states, including New Jersey, turning competitive.

Speaking in the battleground state of Pennsylvania, where polls have the presidential candidates locked in a tight race, Mr. Bush accused Senator Kerry of making wild charges and of demeaning American troops in the field – part of a pattern, Mr. Bush said, of his Democratic rival “saying almost anything to get elected.”

The president raised the possibility of the explosives having been moved before American troops arrived at the Iraqi base where they were stored, Al Qaqaa, around the time Baghdad fell. “This investigation is important, and a political candidate who jumps to conclusions without knowing the facts is not the person you want as your commander in chief,” the president said.

Within minutes of Mr. Bush’s remarks, Mr. Kerry, who was campaigning in Sioux City, Iowa, responded, accusing the president of “dodging and bobbing and weaving” to evade responsibility for the disappearance of the 380 tons of high-grade explosives that had been tagged by the International Atomic Energy Agency months before the invasion of Iraq.

“The missing explosives could very likely be in the hands of terrorists and insurgents, who are actually attacking our forces now 80 times a day on average,” Mr. Kerry said.

Experts say, though, that the types of explosives that are missing have not been used so far in terrorist bombings in Iraq.

The president’s comments broke a two-day silence on the issue of the missing explosives, an issue Mr. Kerry has seized on, and they were welcomed by many senior Republicans. Those supporters expressed dismay at the lack of immediate response from Mr. Bush when the story broke Monday in the New York Times.

Mr. Kerry had mocked the president Tuesday for remaining silent about a story that Republicans argue is a repackaged report first aired by CBS on April 3, 2003, and by the Times the next day.

Republicans said the Times report Monday was part of an effort by news organizations to ambush the president in the final days of the campaign, and they have accused the head of the energy agency, Mohammed ElBaradei, of raising the matter to embarrass Mr. Bush.

The sharpness of yesterday’s exchanges over the explosives issue between the presidential candidates’ camps testified to the desperate fight that is developing between the party tickets, with the blame game mixing with the homestretch ground game that’s likely to decide who wins the White House. National opinion polls have the race tied and suggest that neither candidate has managed to build up momentum. Statewide surveys show plenty of movement but offer little clarity. The result is that party strategists are faced with a complicated Electoral College map.

New state polls suggest the race is deadlocked in the three most important swing states, Florida, Ohio, and Pennsylvania, although one survey published yesterday had the Buckeye State moving toward the president, with a four percentage-point Bush lead there. In Missouri, though, the president appears to be slipping and the race tightening to a too-close-to-call contest, according to a poll for the St. Louis Post-Dispatch.

Several states have joined the list of toss-ups, including – to the surprise of Democrats – New Jersey, Michigan, and Hawaii, a state that has only backed a GOP nominee twice before.

According to a Quinnipiac University poll in the Garden State, Mr. Bush and his Democratic challenger are in a dead heat there. Terrorism concerns and Mr. Bush’s recent campaign stop in the state earlier this month appear to be responsible for the swing to the Republican ticket, with 53% of respondents saying the president is better able to handle the war on terrorism compared to just 37% for Mr. Kerry.

The Democrat, though, is favored when it comes to handling the economy.

“The numbers say it’s tied but it’s in the hands of the undecided voters, in a state that everybody expected Kerry to put away,” Maurice Carroll, director of the Quinnipiac University Polling Institute, told the Associated Press.

In Michigan, too, the president is faring well, again to the surprise and disappointment of the Democrats. Although the economy, hurt by recession, remains the top priority for Michigan voters, the race in the state is now seen as tied, providing support for Mr. Bush’s contention at the start of week, in an interview with ABC News, that to discount Michigan would be a mistake.

Bush campaign advisers were also buoyed yesterday by an ABC News tracking poll suggesting that early and absentee voters are breaking the president’s way by 51% to 47%,although the poll sampling was small and the result well within the margin of error.

With the list of battleground states expanding instead of narrowing, as had been expected, both campaigns are intensifying their efforts to energize their base voters and to boost turnouts and they are redoubling their appeals to undecided voters and to potential defectors. The campaigns are scrapping for anything they can, so that states with few electoral votes are nevertheless attracting considerable attention from the national tickets.

One is New Mexico, which Vice President Gore won four years ago by a mere 366 votes after a recount. Mr. Kerry campaigned in Las Cruces last weekend and was in Albuquerque on Tuesday night. Mr. Bush was in the state three days ago. Neither campaign is ruling out a return visit by the nominee before Tuesday. “The election is going to be decided by who can mobilize and turn out their base,” said Governor Richardson, a Democrat.

Mr. Bush maintained his hunt for conservative Democrat votes, and in Pennsylvania, Ohio, and Michigan yesterday he had Democratic Senator Miller of Georgia accompanying him. Later this week the Bush campaign is airing a 60-second commercial meant to show the president as a compassionate and trustworthy leader for these dangerous times, and using footage of him as he told the Republican National Convention about meeting the children of American soldiers killed in Iraq.

Mr. Kerry was focusing yesterday on the economy while campaigning in Iowa and Minnesota, where he appealed to middle-class voters, saying Mr. Bush had sold them out to help the wealthy and now wanted “four more years so that he can keep up the bad work.”

“This president has failed middleclass families with almost every choice he’s made,” Mr. Kerry said. “He’s given more to those with the most, at the expense of middle-class working families who are struggling to get ahead.”

The question about the missing explosives in Iraq continued to resonate on the campaign trail throughout the day as the party tickets traded barbs. Mr. Bush took up the remarks of a Kerry security adviser, Richard Holbrooke, who in an interview with Fox News said “I don’t know what happened.”

“The senator is making wild charges about missing explosives, when his top foreign-policy adviser admits ‘We do not know the facts,'” Mr. Bush said. “Think about that: The senator is denigrating the actions of our troops and commanders in the field without knowing the facts.”

On Mr. Kerry’s campaign plane yesterday, a top adviser, Michael McCurry, said: “There is a window that’s available there, where either just prior to or just after the invasion, there could have been an opportunity for either Saddam to move the weapons or for something happening after that facility had been abandoned.” Mr. McCurry, a former White House and State Department spokesman, said it was up to the administration to answer what had happened, “but they don’t have an answer.”

A report in the Washington Times cited the deputy undersecretary of defense for international technology security, John A. Shaw, as saying Russian special forces troops moved many of Iraq’s weapons and related goods into Syria in the weeks before the March 2003 U.S. military operation.

Earlier, Democrats pounced on a report in the New York Times, in which the brigade commander of the 101st Airborne troops who arrived at Al-Qaqaa said his soldiers never mounted a real search for weapons at the installation. But the 2003 reports run by the newspaper and by CBS News indicate a search of the facility was mounted.