Jae C. Hong, Associated Press
Democratic presidential candidate Sen. Barack Obama stands onstage as he is introduced to speak in Independence, Mo.

INDEPENDENCE, Mo. — Sen. Barack Obama on Monday rejected the comments from a leading Democrat and campaign military adviser who diminished Sen. John McCain's service as a naval aviator in Vietnam when he declared, "I don't think riding in a fighter plane and getting shot down is a qualification to be president."

As Obama delivered a speech here on patriotism that tried to defuse attacks on his own background, he responded to the remarks of Wesley K. Clark, the retired general and onetime Democratic presidential candidate who suggested on Sunday that McCain had not been tested as a wartime commander.

"For those like John McCain who have endured physical torment in service to our country, no further proof of such sacrifice is necessary," Obama said. "And let me also add that no one should ever devalue that service, especially for the sake of a political campaign — and that goes for supporters on both sides."

Asked if he wanted an apology, McCain said, "That's certainly up to Senator Obama." Later, he added, "I know that General Clark's comment is not an isolated incident."

The terse exchanges between the rivals, echoed even more vociferously by their campaign representatives and surrogates, underscored a central question both candidates are grappling with: How do they present themselves as practicing a new kind of politics, while they, and particularly their allies, are still pointing out flaws in each other?

Obama arrived here in Independence, the home of President Harry S. Truman, to open a weeklong patriotism tour. He sought to explain and defend his American ideals to ward off skepticism and silence persistent rumors about his loyalties to the nation.

"I will never question the patriotism of others in this campaign," Obama said, speaking over the applause of hundreds of supporters. "And I will not stand idly by when I hear others question mine."

Yet Obama's effort to highlight his American values, delivered in a 30-minute address before a backdrop of flags, was complicated by the comment from Clark. The war record of McCain once seemed like an unassailable asset to his presidential bid, but Clark's comments on the CBS News program "Face the Nation" — that being shot down in Vietnam was not a qualification to be president — raised the possibility that McCain's military record would face scrutiny.

Clark, who was a leading supporter of Sen. Hillary Rodham Clinton, was named in June to a group of national security advisers to the Obama campaign.

On Monday afternoon, Obama declined to answer reporters' questions about Clark, but a spokesman said: "Senator Obama honors and respects Senator McCain's service, and of course he rejects yesterday's statement by General Clark."

McCain has had to distance himself from remarks criticizing Obama's patriotism, particularly television advertisements from the Republican parties in several states. It was Obama on Monday who had sought to answer those questions about his own background even as he distanced himself from comments questioning McCain's service.

As he campaigned in Pennsylvania, McCain said he thought remarks like Clark's were "unnecessary."

In a conference call, a number of McCain's former colleagues in the military and former prisoners of war in Vietnam also stood by his record and assailed Clark for impugning McCain's heroism.

Sen. John W. Warner, R-Va., a former Navy secretary and former Armed Services Committee chairman, said he was "utterly shocked" at Clark's comments.

Warner said it was "an exercise in poor judgment" for the Obama campaign to employ Clark as a surrogate.

For his part, Obama vowed to fight back against conservative critics who have questioned his patriotism "to score political points and raise fears about who I am and what I stand for."

The speech was the latest attempt by the campaign to fight back against incorrect assertions that Obama will not recite the Pledge of Allegiance, place his hand over his heart during the national anthem or wear a flag pin on his lapel. (He began wearing a pin two months ago after the criticism failed to subside.)

Obama sought to place his criticism into a broader context of American history, pointing out that Thomas Jefferson was accused by the Federalists of "selling out to the French," and John Adams was derided for being "in cahoots with the British."

"The use of patriotism as a political sword or a political shield is as old as the Republic," Obama said.

In his campaign against McCain, Obama does not have the biography of a military record to offer as a validation of his patriotism, so his weeklong tour through several Republican-leaning states was intended to introduce himself to voters.