WASHINGTON — Senator Obama’s campaign, in advance of the candidate’s speech to America’s largest pro-Israel lobby, is highlighting the candidate’s support for designating Iran’s Revolutionary Guard forces as a foreign terrorist organization.

Senator McCain, in his speech yesterday to the American Israel Public Affairs Committee, criticized Mr. Obama for opposing a nonbinding resolution designating Iran’s primary military organization as terrorists. The Obama campaign responded that their problem with that resolution, sponsored by senators Kyl and Lieberman, had not been the designation of the Iranian guard as a terrorist group, but the idea that it committed American troops in Iraq to countering Iranian influence.

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The shift, at least in emphasis, from the Obama campaign marks a new approach for the candidate, who has been backing away from his pledge to meet with Iran’s president and who is now attacking Mr. McCain and President Bush on the grounds that Iran and affiliated terror groups have been strengthened as a result of the Iraq war. It could signal that Mr. Obama is turning his attention away from the Democratic primary battle against Senator Clinton, which draws to a close with the final contests today in Montana and South Dakota, and putting his focus on the general election, in which the Democratic nominee will face the Republican, Mr. McCain.

“We had a fulsome debate on this in the Senate,” the Obama campaign’s senior foreign policy director, Denis McDonough, said on a conference call with reporters, referring to the Kyl-Lieberman resolution. “Obama continued to support this position though. The debate last fall was about the broader implications and other parts of that amendment, giving the soldiers an additional mission in Iraq.”

Mr. McDonough pointed to Mr. Obama’s sponsorship of the Iran Counter-Proliferation Act, “which would designate the Iranian Revolutionary Guards a terrorist organ,” according to an e-mail sent out by the campaign, as well as “prohibit trade with Iran, freeze Iranian officials’ assets and help combat terrorist financing.”

Mr. McCain said yesterday, “I was pleased to join Senators Lieberman and Kyl in backing an amendment calling for the designation of the Revolutionary Guard as a terrorist organization responsible for killing American troops in Iraq.”

Mr. McCain went on, “Over three quarters of the Senate supported this obvious step, but not Senator Obama. He opposed this resolution because its support for countering Iranian influence in Iraq was, he said, a ‘wrong message not only to the world, but also to the region.'”

American forces in Iraq currently work closely with Iraq’s Sunni intelligence service to attack Iran’s terror network in Iraq. The Marines and Army have arrested and detained dozens of Quds Force officers and other suspected Iranian agents in Iraq.

When asked whether Senator Obama supported this aspect of the current mission in Iraq, Mr. McDonough said, “Obviously Barack is very concerned about the threats posed to our troops in Iraq as a result of support provided by Iranian entities. I do mention that General Petraeus underscored this last week as well.” Mr. McDonough said that Mr. Obama has favored diplomacy with Iran to resolve the issue. This approach is recommended by the bipartisan Iraq Study Group and has been tried three times by Ambassador Crocker in Baghdad with little to show for the discussions.

The Illinois senator has also said that he thinks the presence of American troops in Iraq has ended up strengthening Iran. This view, held also by the House and Senate Democratic leadership, was disputed last month in written testimony from General Petraeus in response to questions from his nomination hearing for his promotion as commander of Central Commander. “The presence of U.S. troops in Iraq and elsewhere in the region has the potential to counter malign Iranian influence against the Government of Iraq, build common cause in the region, and expose the extent of malign Iranian activities to the world,” he wrote.

Mr. Obama has chosen to emphasize his position that he would authorize diplomacy with Iran without requiring the mullahs to end their enrichment of uranium. He has also supported sanctions on foreign companies that invest in Iran’s economy.

Mr. McCain yesterday emphasized that diplomatic outreach with the Iranians has been tried in the past and has failed, as in the case of the Clinton administration’s efforts to reach out to Mohammed Khatami.

“We hear talk of a meeting with the Iranian leadership offered up as if it were some sudden inspiration, a bold new idea that somehow nobody has ever thought of before,” he said. “Yet it’s hard to see what such a summit with President Ahmadinejad would actually gain, except an earful of anti-Semitic rants, and a worldwide audience for a man who denies one Holocaust and talks before frenzied crowds about starting another.”

The Iranian president, true to form, predicted Monday, “the Zionist regime, with a 60-year record of genocide, plunder, invasion and betrayal is about to die and will soon be erased from the geographical scene.” Pope Benedict XVI said yesterday he would not meet with Mr. Ahmadinejad when the Iranian president arrives in Rome for a world hunger conference sponsored by the United Nations.

Mr. McCain, in his remarks at Aipac, made a point to praise Democrats who have supported the American relationship with Israel, such as Senator Henry “Scoop” Jackson, who died in 1983. “In 1979, I traveled with him to Israel, where I knew he was considered a hero,” Senator McCain said. “But I had no idea just how admired he was until we landed in Tel Aviv, to find a crowd of seven or eight hundred Israelis calling out his name, waving signs that read ‘God Bless you, Scoop’ and ‘Senator Jackson, thank you.'”

The praise for Democrats like Mr. Jackson was the one portion of Mr. McCain’s speech Mr. McDonough complimented. “He mentioned of course Senator Jackson, about whom we all very proud,” he said.