Denver —- Sen. John McCain, the presumptive Republican presidential nominee, distanced himself from the Bush administration on Tuesday by vowing to work more closely with Russia on nuclear disarmament and by calling for a reduction in tactical nuclear weapons.

In what his campaign promoted as a major speech on nuclear security policy, McCain told a crowd at the University of Denver that he supported a legally binding accord between the two nations to replace verification requirements in the Strategic Arms Reduction Treaty, or START, which expires in 2009. The Bush administration has refused to accept such binding limits on nuclear weapons, which the administration's critics say has created paranoia in Moscow.

"Russia and the United States are no longer mortal enemies," McCain said in a speech that was interrupted at least four times by hecklers opposed to the Iraq war. "As our two countries possess the overwhelming majority of the world's nuclear weapons, we have a special responsibility to reduce their number. I believe we should reduce our nuclear forces to the lowest level we judge necessary, and we should be prepared to enter into a new arms control agreement with Russia reflecting the nuclear reductions I will seek."

McCain took an oblique but direct swipe at opponent Barack Obama and his stated willingness to meet with the leaders of America's greatest enemies, including North Korea and Iran. "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," McCain said.

Obama had called in October for "a world in which there are no nuclear weapons," a fact his campaign underscored Tuesday.

"By embracing many aspects of Barack Obama's nonproliferation agenda today," said a statement from Obama's spokesman, Bill Burton, "John McCain highlighted Obama's leadership on nuclear weapons throughout this campaign. ... No speech by John McCain can change the fact that he has not led on non-proliferation issues when he had the chance in the Senate."