WASHINGTON (AP) _ Democrat Barack Obama pressed ahead with attempts to burnish his foreign policy credentials, appearing with two party heavyweights and potential vice presidential picks for an exhaustive outline of his plans to keep America safe — especially from nuclear, biological and cyber attacks.

Obama pointedly chose Purdue University, a top institution in the American Midwest, for its location in Indiana, historically a Republican bastion where he is trying to engineer a Democratic breakthrough. He was joined by the state's popular Democratic Sen. Evan Bayh and former Georgia Democratic Sen. Sam Nunn, one of the country's top experts on nuclear issues, especially weapons proliferation.

Both men have been mentioned as possible running mates, but could also prove valuable in helping him make inroads in traditionally Republican states like those in the U.S. South.

As Obama campaigned relentlessly to overcome attempts by Republican opponent John McCain to paint him as naive and untested on foreign policy issues, the four-term Arizona senator spoke to the National Association for the Advancement of Colored People convention in Cincinnati, Ohio, promising to boost educational opportunities for students in failing schools, many of which are in black communities.

McCain was received politely by members of America's oldest civil rights organization. Obama, who would be the first African-American president in U.S. history, was given a hero's welcome by convention-goers three days earlier.

McCain told the civil rights organization that he will expand education opportunities, partly through vouchers for low-income children to attend private school.

The Arizona Republican praised Obama's historic campaign, but faulted the Illinois senator on his education policy, saying he is wrong to oppose school vouchers for students in failing public schools.

McCain said vouchers and other tools such as merit pay for teachers are needed in order to break from conventional thinking on educational policy.

Obama has spoken in favor of performance-based merit pay for individual public school teachers. In a speech last year he told the National Education Association, the country's largest teachers union, that the idea should be considered.

McCain also praised Martin Luther King, Jr., as a leader who "loved and honored his country even when the feeling was unreturned, and counseled others to do the same."

In praising King to the NAACP, McCain used similar language to his mea culpa in April on the 40th anniversary of the civil rights leader's assassination, saying he had been wrong to vote against a federal holiday honoring King.

Meanwhile Obama, fighting perceptions that McCain is better prepared to deal with issues of foreign policy and national security, outlined his blueprint for keeping the country safe. Two goals of his administration, he said, would be securing all loose nuclear material during his first term and ridding the world of nuclear weapons.

He said adhering to nonproliferation treaties pressure nations such as North Korea and Iran. North Korea has tested a nuclear weapon, and Iran has an energy program the Bush administration warns could be a precursor to nuclear weapon development.

The Democrat called for investing in methods to prevent, detect and contain biological attacks and said he would appoint a national cyber security adviser. He highlighted a proposal to spend $5 billion over three years to develop an international intelligence and law enforcement infrastructure to stymie terrorist networks.

"The danger ... is that we are constantly fighting the last war, responding to the threats that have come to fruition, instead of staying one step ahead of the threats of the 21st century," Obama said.