Former president Bill Clinton, hitting the campaign trail with Sen. John F. Kerry less than seven weeks after emergency heart surgery, accused the Bush administration today of playing on voters' fears and urged Americans instead to "vote for the person who wants you to think and hope."

Addressing a large rally in Philadelphia before introducing the Democratic presidential candidate, Clinton highlighted what he said were the stark choices facing voters in the Nov. 2 election and contrasted the achievements of his own eight-year administration with what he described as President Bush's failures and misguided policies.

As he and Kerry took to the stage, a roar went up from the thousands of union members and other supporters hoisting American flags and campaign signs, a crowd evidently swelled by Clinton's first campaign appearance since undergoing a quadruple bypass in New York on Sept. 6.

"If this isn't good for my heart, I don't know what is," said Clinton, 58. After thanking well-wishers, he added, "From time to time I've been called the comeback kid. In eight days, John Kerry is going to make America the comeback country."

Appearing slimmer than before his surgery, Clinton said the Bush administration has foisted on future generations the cost of cutting taxes for the wealthiest Americans, himself included.

"We don't want our children and our grandchildren paying for the cost of our tax cuts," he said. He also criticized the administration's policies on health care, education and homeland security, saying Kerry can do better.

"Their policy is to take 88,000 cops off the street and put the assault weapons back on," Clinton said. "John Kerry's got a better idea." He said that as president, the Massachusetts senator "will give us a larger army," put more emphasis on homeland security and do a better job of preventing nuclear proliferation and going after the al Qaeda terrorist network.

"In the closing days of this election," the Republicans are "trying to scare the undecided voters about Senator Kerry, and they're trying to scare the decided voters away from the polls," Clinton said.

"Now one of Clinton's laws of politics is this: If one candidate's trying to scare you and the other one's trying to get you to think, if one candidate's appealing to your fears and the other one's appealing to your hopes, you better vote for the person who wants you to think and hope."

Kerry attacked Bush as incompetent for failing to secure hundreds of tons of highly explosive materials in Iraq that he said now could be in the hands of terrorists.

"Our country and our troops are less safe because this president failed to do the basics," Kerry told the crowd. "The unbelievable incompetence of his administration step after step has put our troops at greater and greater risk, over-extended the American military, isolated the United States [and] put a greater financial burden on the American people."

The comments came as Bush and Kerry launched the last full week of their presidential campaigns today with rallies in closely contested states and appearances on morning talk shows that highlighted their widely divergent views on the war in Iraq.

Addressing supporters in Greeley, Colo., Bush made no mention of the missing explosives. Nor did he answer any questions from reporters, even the small pool that travels with him. Although he has given a few interviews, Bush has not answered questions from his press corps since he appeared in the Rose Garden with Iraq's interim prime minister, Ayad Allawi, just over a month ago, on Sept. 23.

The revelation of the missing explosives appeared to pose both immediate and long-term problems for the Bush campaign. The story, along with Kerry's appearance with Clinton, dominated television news on a day when Bush was barnstorming with former New York mayor Rudolph W. Giuliani and delivering what his staff had billed as a major new speech about terrorism, laced with fresh attacks on Kerry.

More broadly, Democrats contended that the revelation undercut two central tenets of Bush's campaign: that the invasion of Iraq had made the United States and the world safer, and that the American people can trust him and his administration to protect the nation from attack.

In his speech, Bush charged that Kerry "has a strategy of pessimism and retreat" in Iraq. Kerry has called the war there "a mistake, a diversion, a colossal error," Bush said. "Then he says he's the right man to win the war. You cannot win a war you do not believe in fighting."

By talking about withdrawing U.S. troops from Iraq during a first term, Kerry "sends the wrong message" to Iraqis and to troops of the U.S.-led coalition, Bush said. "My opponent has the wrong strategy for the wrong country at the wrong time," he said. "On this vital front in the war on terror, protest is not a policy, retreat is not a strategy, and failure is not an option."

Bush also asserted that during a 20-year Senate career, "in key moments of challenge and decision for America, Senator Kerry has chosen the position of weakness and inaction." He coupled the charge with an appeal for votes from Democrats.

"With that record, he stands in opposition not just to me, but to the great tradition of the Democratic Party," Bush said. "The party of Franklin Roosevelt and Harry Truman and John Kennedy is rightly remembered for confidence and resolve in times of war and in hours of crisis. Senator Kerry has turned his back on 'pay any price' and 'bear any burden.' And he has replaced those commitments with 'wait and see' and 'cut and run.' "

Giuliani said in introducing Bush that in order "make certain that we continue to remain on offense [against terrorists], we need to reelect President Bush and Vice President Cheney."

The best news for the White House today was that Colorado, a state that Bush won by 9 percentage points in 2000 but that had begun to look competitive for Kerry, had solidified firmly enough for Bush that Kerry no longer plans to advertise heavily in the state.

"They've given up," White House communications director Dan Bartlett crowed. "They wasted their trip here last week."

Bush scheduled an appearance today in Iowa after his speech in Colorado, while Kerry was due to visit Michigan and Wisconsin after his appearances in New Hampshire and Pennsylvania.

Clinton, interviewed on ABC this morning, said he decided to give a campaign speech with Kerry at the senator's request because the race between the senator and Bush is so tight, "and because I think it's important and because the differences between the two candidates and the courses they'll pursue in the next four years are so profound."

Asked if Kerry could win, Clinton said, "I think so, but it's very close. Our country is divided culturally pretty evenly now: Each party has a base vote of about 45 percent. So the election will turn on what percentage of that 45 percent shows up, who's done a better job of registering and what percentage shows up, and then how the other 10 percent sees it. And I think this is really one of the most difficult elections to call I've ever seen."

Clinton, who had quadruple bypass surgery less than seven weeks ago, said, "I feel good. My chest is normally a little tender in the morning. And I get up and walk around and start moving around I feel better immediately."

He said he felt "blessed" that his wife, Sen. Hillary Rodham Clinton (D-N.Y.), and their daughter Chelsea have stayed with him at home in Chappaqua, N.Y., a lot. "And I just sleep and walk, read books, watch baseball. That's what I do."

Kerry said on NBC's "Today" show in an interview taped Sunday that "we haven't done a third of the things that we need to do to win the war on terror," and he vowed, "I am going to make America safer and stronger than George Bush has."

Asked what Clinton would bring to his campaign, said, "Well, obviously, I hope he brings the strength of health and just the excitement that Bill Clinton always brings to the campaign trail. This was a very successful president in terms of policies of our country . . . . We balanced the budget. We paid down the debt for two years in a row. . . . We raised the minimum wage for people. All things George Bush has undone or not done."

Kerry said he was not concerned that Clinton, who was embroiled in a sex scandal during his presidency, might alienate some voters.

"I am running for president, not Bill Clinton," Kerry said. "But Bill Clinton's policies made a difference to the lives of Americans. And I want to remind Americans that there are better choices than George Bush is making."

Bridling at charges by Bush and Vice President Cheney that he is weak on national security, Kerry referred to his Vietnam War service. "Unlike Dick Cheney and George Bush, I put my life on the line for my country when it counted," Kerry said. "I fought for this nation and I defended it as a young man. And I will defend America as president of the United States."

He said he has supported the largest military and intelligence budgets in U.S. history. "And I'm not going to take a second seat to anybody about the passion that I bring to defending America."

In an interview on ABC's "Good Morning America" that was taped at his Crawford, Tex., ranch over the weekend, Bush refused to concede the prospect of defeat in the election and insisted that the costs of the war in Iraq -- in U.S. casualties and funding -- have been "worth it."

Bush said that "I think this race is a nonpredictable race" and that some unexpected states would be "in play." But asked whether, in his private moments, he contemplated losing the election, Bush answered, "I'm not there yet. . . . I believe I'm going to win. And I'm campaigning as if we are going to win."

As for whether -- in view of 1,100 U.S. dead, 8,000 more wounded and the expenditure of $140 billion and counting in Iraq -- there comes a point "where the cost is too great," Bush replied, "Yes, the cost is too great if the American president withdraws before the mission is complete. . . . And the mission is to help Iraq become a free nation in the midst of the greater Middle East."

Bush added, "I spent a lot of time thinking about, as you said, the risk/reward and concluded that the benefits to our country, short term and long term, were worth it."

Asked if it would still be worth it if the United States loses another 1,000 troops and he has to request $50 billion or $60 billion more for Iraq after the election, Bush said, "It's essential that we succeed in Iraq at this point. . . . It's essential, because if we do not succeed in Iraq, one, the terrorists will rejoice and be emboldened. This is a global war."

Vice President Cheney also hit the national security theme hard during a town hall gathering in Minnesota this morning, telling voters that the country has reached a "breaking point in American history" where it must set the course of national security for the next 30 to 40 years, Washington Post staff writer Lyndsey Layton reported.

"The biggest threat we'll face today is . . . a group of these terrorists in one of our cities with the kind of deadly capability we're talking about," said Cheney, mentioning chemical, biological and nuclear weapons. The vice president made the comments as he sat on a stool next to his wife, Lynne, on the basketball court at Minnesota State University in Moorehead.

Cheney said Bush has a plan to defeat the terrorists abroad and keep them from again attacking Americans on U.S. soil, but that he has "serious doubts whether John Kerry, based on his record, would pursue that kind of strategy to keep America safe."

In defending the war in Iraq, Cheney said that "Iraq, in our minds, represented the greatest likelihood of nexus, if you will, between, on the one hand, the terrorists, and on the other hand, that deadly technology developed over the years by Saddam Hussein."

The theme resonated with audience members such Mike and Gladys Mickelson, both 76-year-old retirees from nearby Fargo, North Dakota. The couple said they were worried about the specter of a terrorist attack in Fargo. "The whole country is very concerned about it happening," Mike Mickelson said.

President Bush lost Minnesota in 2000 to Al Gore by less than 2.5 percentage points. A growing conservatism in suburbs and rural areas has fueled hopes by the Bush campaign that it might win the state's 10 electoral votes. This morning's event was kicked off by Sen. Norm Coleman (R), who beat one of Minnesota's best-known Democrats, Walter Mondale, to win the Senate seat held by the late Paul Wellstone (D).

Allen, traveling with Bush, reported from Colorado.