WASHINGTON — Senator McCain is promising to enter into new agreements with Russia aimed at reducing the two largest nuclear arsenals left on the planet and to renegotiate the terms of the Nuclear Nonproliferation Treaty, the compact the U.N. Security Council has said Iran is violating through its continued enrichment of uranium.

The emphasis on arms control, in a speech yesterday at the University of Denver, marked a rhetorical departure for the presumptive Republican nominee, who has been tougher on Moscow on the campaign trail than Senator Obama or President Bush. In March, Mr. McCain proposed ousting Russia from the Group of Eight industrialized nations.

The speech was also an apparent dig at the Bush administration, which failed to change the nonproliferation treaty at an international conference in 2006 and has pursued some weapons programs that Mr. McCain says he opposes. Yesterday evening, Mr. McCain attended a private fund-raiser with Mr. Bush in Phoenix; the president is scheduled to attend two private McCain events today in Utah.

Referencing a speech by President Reagan in which the former leader spoke of his “dream” of a world free of nuclear weapons, Mr. McCain said: “That is my dream, too. It is a distant and difficult goal. And we must proceed toward it prudently and pragmatically, and with a focused concern for our security and the security of allies who depend on us.”

Specifically, Mr. McCain said he would take Russia up on its offer to negotiate an end to intermediate-range nuclear weapons, which can travel between 300 and 3,400 miles.

If elected president, Mr. McCain said, he would seek to change the terms of the Nuclear Nonproliferation Treaty to punish any country, such as North Korea and Iran, that illicitly seeks fissile material without notifying the International Atomic Energy Agency.

“The IAEA shouldn’t have to play cat-and-mouse games to prove a country is in compliance,” he said. “It is for suspected violators to prove they are in compliance. We should establish a requirement by the U.N. Security Council that international transfers of sensitive nuclear technology must be disclosed in advance to an international authority such as the IAEA, and further require that undisclosed transfers be deemed illicit and subject to interdiction. Finally, to enforce treaty obligations, IAEA member states must be willing to impose sanctions on nations that seek to withdraw from it.”

Mr. McCain said that, as president, he would consider changes to the Comprehensive Nuclear Test Ban Treaty, a pact he opposed in 1999, that would make the Senate more likely to support it. He also said he would seek unilaterally to reduce America’s nuclear arsenal, including the Robust Nuclear Earth Penetrator, a program opposed by Congress but supported by the Bush administration.

The Arizona lawmaker also said he favored the creation of an international repository where all spent nuclear fuel could eventually be sent. Taking a position that could win him votes in Nevada, he said: “It is even possible that such an international center could make it unnecessary to open the proposed spent nuclear fuel storage facility at Yucca Mountain in Nevada.”

Mr. McCain also took a shot at his likely rival in the election, Mr. Obama. “Today, some people seem to think they’ve discovered a brand new cause, something no one before them ever thought of,” he said. “Many believe all we need to do to end the nuclear programs of hostile governments is have our president talk with leaders in Pyongyang and Tehran, as if we haven’t tried talking to these governments repeatedly over the past two decades.”

Mr. Obama recently defended his statement that he would seek high-level talks with Iran, even if it continues enriching uranium. Mr. Bush has said he will not consider any high-level engagement with Tehran unless it suspends enrichment.

But Mr. McCain also said that force should only be considered as a last resort: “Others think military action alone can achieve our goals, as if military actions were not fraught with their own terrible risks. While the use of force may be necessary, it can only be as a last resort, not a first step.”

A spokesman for Mr. Obama, Bill Burton, said in response to the speech that Mr. McCain had stolen many of the Illinois senator’s ideas.