WASHINGTON — In a break with his party and President Bush, Senator McCain is throwing his support behind a federal law that aims to protect a journalist’s right to conceal confidential sources from the courts.

The presumptive Republican nominee announced his position on the Free Flow of Information Act, or federal shield law, yesterday at the annual meeting of the Associated Press.

The shield law, which still allows for courts in some national security cases to demand testimony on confidential sources from journalists, has been championed by press freedom groups. Some studies show a tenfold increase in the number of journalists subpoenaed before the courts since 2001. Most notable in that group is a former New York Times reporter, Judith Miller, who in 2005 was forced to hand over her notes of conversations with Vice President Cheney’s chief of staff, I. Lewis Libby.

In his remarks, Mr. McCain said he was wary that the new law could be a “license to do harm, perhaps serious harm.” He said also that he believed that the New York Times crossed a line when it published details about a secret National Security Agency surveillance program aimed at intercepting communications between Al Qaeda operatives abroad and Americans.

But despite these risks, the Arizona lawmaker said the proposed law was also a “license to do good; to disclose injustice and unlawfulness and inequities; and to encourage their swift correction.” He said that if he had to vote on the bill today, he would vote in favor of it.

Mr. McCain’s position on the shield law is the same as the two Democratic senators contending for their party’s presidential nomination. Spokesmen yesterday for both the Clinton and Obama campaigns said the Democratic candidates supported the Free Flow of Information Act. Senator Obama was an initial co-sponsor of the bill currently before the Senate. The position of the presidential candidates contrasts not only with that of the White House but also with views expressed by the heads of most of the executive branch agencies and departments that deal in classified information. The Department of Justice on its Web site has devoted a special page to posting letters to Congress from these department heads opposing the bill.

The latest such letter, written April 7 by Secretary of Energy Bodman, said, “Regardless of who bears responsibility for the occurrence of the initial security breach or loss of classified data, there can be no doubt that once such a breach has occurred, it is in the national security interest of the United States to ascertain how, when, and why the breach or loss occurred, to ascertain and limit the damage caused, and to prevent such breaches or losses in the future.” Ms. Miller yesterday said she welcomed Mr. McCain’s endorsement. “I believe that the measure, as currently worded, goes out of its way to ensure that America’s national security interests will be protected. Without a federal shield law, it’s an independent, free press that is now vulnerable,” she said.

Mr. McCain yesterday also seized on remarks made last week by Mr. Obama at a fundraiser in San Francisco suggesting that rural Americans “cling” to guns and religion because of bitterness about the loss of industrial jobs. “On the contrary,” Mr. McCain said. “Their faith had given generations of their families purpose and meaning, as it does today. And their appreciation of traditions like hunting was based in nothing other than their contribution to the enjoyment of life.”

Mr. Obama, who has been defending himself over those remarks for the past three days, tried to turn the tables, saying that Americans were bitter about the failure of national politicians to address the effects of economic globalization. “Now, Senator McCain and the Republicans in Washington are already looking ahead to the fall and have decided that they plan on using these comments to argue that I’m out of touch with what’s going on in the lives of working Americans,” he said in a separate appearance before the Associated Press group. “I don’t blame them for this — that’s the nature of our political culture, and if I had to carry the banner for eight years of George Bush’s failures, I’d be looking for something else to talk about, too,” Mr. Obama said.

Mr. Obama was asked by the chairman of the Board of the Associated Press, William Dean Singleton, whether he favored shifting troops from Iraq to fight “Obama bin Laden.” Mr. Obama corrected Mr. Singleton and said, “I think that was Osama bin Laden.” He then took a drink of water. Mr. Singleton apologized. Mr. Obama then said, “No, no, no this is part of the exercise that I’ve been going through over the last 15 months, which is why it’s pretty impressive I’m still standing here.”