Senator McCain declined to disavow today the tough criticism by his campaign of his Democratic opponent’s experience as a community organizer, saying politics is “tough business” even as he praised Senator Obama’s service.

At a live, televised forum on public service timed to coincide with the anniversary of the 2001 terrorist attacks, Mr. McCain said he respected Mr. Obama’s decision after law school to forgo a lucrative career path and become a community organizer in downtrodden Chicago.

“I respect people who serve their community,” Mr. McCain said. “And Senator Obama’s record there is outstanding.”

He also paid tribute to Mr. Obama for inspiring “millions of Americans who otherwise wouldn’t have been involved in the political process”, while giving himself credit for attracting voter turnout with “my record of service and my vision for the future.”

At the same time, Mr. McCain said the negativity that has infused the presidential race — on hiatus for one day in honor of the Sept. 11 anniversary — could have been avoided had Mr. Obama accepted his proposal for the two to tour the country together doing town-hall meetings, a format in which Mr. McCain shines best.

“I think the tone of this whole campaign would have been very different,” the GOP nominee said during the Service Nation Presidential Candidates Forum, held at Columbia University.

Mr. McCain was followed to the stage by his Democratic opponent, Mr. Obama, and they shook hands and hugged quickly before Mr. McCain departed.

The event amounted to back-to-back live interviews of the two candidates — the forum was broadcast live on some cable networks — by Judy Woodruff of PBS’ “NewsHour” and the managing editor of Time magazine, Richard Stengel. The 1,000-member audience included relatives of victims of the September 11th attacks, veterans, policy leaders, students, and celebrities such as Caroline Kennedy, R&B singer Usher, and actors Tobey Maguire and Leonardo DiCaprio.

Recently, McCain campaign surrogates derided Mr. Obama’s experience as too thin to qualify him for the White House. But that line of attacked subsided somewhat after Mr. McCain chose as his running mate, Sarah Palin, a former small-town mayor who has been Alaska’s governor for less than two years.

“This is a tough business,” he said. “Has it been rough? Of course.”

He added: “The people make the final judgment with their votes.”

Mr. McCain also said he would have asked Americans to serve after the 2001 terrorist attacks by joining neighborhood watches or helping guard nuclear plants, offering an implicit criticism of President Bush’s approach seven years ago.

Mr. Bush has been criticized for a speech given about two weeks after the Sept. 11 attacks, in which he exhorted the public to “do your business around the country, fly and enjoy America’s great destination spots, get down to Disney World in Florida.” Though Bush emphasizes the importance of volunteerism and service, he didn’t ask Americans to respond to the attacks — or to participate in the Iraq war — through personal sacrifice.

Mr. Obama has promised that a call to service would be a cornerstone of his presidency, and also has criticized Bush for asking Americans eager to pitch in after the attacks merely “to shop.”

The expansion of government national service programs he has proposed would cost $3.5 billion a year, including a new “Green Vet Initiative,” increasing the all-volunteer military, expanding AmeriCorps, doubling the size of the Peace Corps, expanding service programs involving retired people, and creating a tax credit making the first $4,000 of college tuition free for students who conduct 100 hours of public service a year.

Mr. McCain, asked about Mr. Obama’s proposal, said: “I’d be glad to spend money.” But he quickly added that “it doesn’t always have to be run by the government.”