President Bush and Sen. John F. 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 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."

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 Nov. 2 election and insisted that the costs of the war in Iraq -- in U.S. casualties and funding -- have been "worth it."

Kerry, the Democratic challenger from Massachusetts, 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."

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

In Philadelphia, Kerry was appearing with former president Bill Clinton, who was making his first campaign appearance since undergoing emergency heart surgery last month.

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, asked on NBC 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 his appearance in Colorado, Bush refined his standard stump speech, using some new language to denounce Kerry and question his credentials to be commander in chief.

By talking about withdrawing U.S. troops from Iraq during a first term, Kerry "sends the wrong message to Iraqis, who need to know that America will not cut and run," Bush said. And he "sends the wrong message to the troops of our coalition, who need to know we will honor their sacrifice by completing the mission."

Bush said, "My opponent has the wrong strategy for the wrong country at the wrong time. 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."

In the interview on ABC, 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 $140 billion and counting spent 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."