HONOLULU (AP) ― President Barack Obama lobbied the skeptical leaders of Russia and China for support in keeping Iran from becoming a nuclear-armed menace to the world, hoping to yield a “common response” to a deepening problem.

Yet Obama’s talk of solidarity with Russian President Dmitry Medvedev and Chinese President Hu Jintao was not publicly echoed by either man Saturday as Iran moved anew to the fore of the international stage ― and to the front of the fierce U.S. presidential race.

The United States’ vast worries about Iran grew starker with a report this week by the U.N. atomic agency that asserted in the strongest terms yet Iran is conducting secret work with the sole intent of developing nuclear arms. The U.S. claims a nuclear-armed Iran could set off an arms race among rival states and directly threaten Israel.

Russia and China remain a roadblock to the United States in its push to tighten international sanctions on Iran. Both are veto-wielding members of the U.N. Security Council and have shown no sign the new report will change their stand.

With Medvedev on the sidelines of an Asia-Pacific summit here, Obama said the two “reaffirmed our intention to work to shape a common response” on Iran.

Shortly after, Obama joined Hu, in a run of back-to-back diplomacy with the heads of two allies that hold complicated and at times divisive relations with the United States.

Speaking to reporters before he talked to Hu, Obama said that he and the Chinese leader want to ensure that Iran abides by “international rules and norms.”

Obama’s comments were broad enough to portray a united front without yielding any clear indication of progress. Medvedev, for his part, was largely silent on Iran during his remarks, merely acknowledging that the subject was discussed. Hu did not mention Iran at all.

As the president held forth on the world stage in his home state, Republicans vying to compete against Obama for the presidency unleashed withering criticism in a debate in South Carolina. It was a rare moment in which foreign policy garnered attention in a campaign dominated by the flagging U.S. economy.

“If we re-elect Barack Obama, Iran will have a nuclear weapon. And if you elect Mitt Romney, Iran will not have a nuclear weapon,” said Romney, the former Massachusetts governor. Minnesota Rep. Michele Bachmann warned that Iran’s attempt to develop a nuclear weapon is setting the table “for worldwide nuclear war against Israel.”

Iran has insisted its nuclear work is in the peaceful pursuit of energy and research, not weaponry.

U.S. officials have said the report by the International Atomic Energy Agency was unlikely to persuade China and Russia to support tougher sanctions on the Iranian government. But led by Obama, the administration is still trying to mount pressure on Iran, both through the United Nations and its own, for fear of what may come should Iran proceed undeterred.

More broadly, Obama sought Saturday to position the United States as a Pacific power determined to get more American jobs by tapping the explosive potential of the Asia-Pacific.

For businesses, he said, “this is where the action’s going to be.” “There is no region in the world that we consider more vital than the Asia-Pacific region,” he told chief executives gathered for a regional economic summit.

The president went so far as to saying the United States had grown “a little bit lazy” in trying to attract business to the United States.

Underscoring the search for some good economic news ahead heading toward a re-election vote, Obama announced the broad outlines of an agreement to create a transpacific trade zone encompassing the United States and eight other nations. He said details must still be worked out, but said the goal was to complete the deal by next year.

“The United States is a Pacific power and we’re here to stay,” Obama said.

The eight countries joining the U.S. in the zone would be Australia, Brunei, Chile, Malaysia, New Zealand, Peru, Singapore and Vietnam. A central topic for Obama and Japanese Prime Minister Yoshihiko Noda was Japan’s interest in joining the trade bloc.

In a sign of potential tension with China, Mike Froman, a deputy national security adviser who focuses on international economic matters, shrugged off complaints from China that it had not been invited to join the trade bloc.

He told reporters that China had not expressed interest in joining and said the trade group “is not something that one gets invited to. It’s something that one aspires to.”