Democratic presidential candidate John Kerry (search) on Tuesday outlined measures he contended would dramatically reduce the possibility that terrorists could attack the United States with nuclear weapons, which he called the greatest threat facing the nation.

"We need to employ a layered strategy to keep the worst weapons from falling into the worst hands," Kerry said in an appearance at the Port of Palm Beach in Riviera Beach, Fla.

Kerry called for building and leading a new era of alliances, modernizing the U.S. military, making full use of American diplomatic, intelligence and economic power, and freeing the nation from its dependence on Mideast oil.

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"If we secure all bomb-making materials, ensure that no new materials are produced for nuclear weapons, and end nuclear weapons programs in hostile states like North Korea and Iran, we will dramatically reduce the possibility of nuclear terrorism," he said.

Kerry said securing weapons and materials in the former Soviet Union would be a priority in relations between the United States and Russia, and he proposed working with U.S. allies to establish global standards for safekeeping nuclear materials. As president, Kerry said, he would also lead an international coalition seeking a global ban on production of material for new nuclear weapons.

To help reduce existing stocks of nuclear materials and weapons, the United States should stop developing a new generation of nuclear weapons and speed up reductions in the U.S. and Russian nuclear arsenals, Kerry said.

Ending nuclear weapons programs in Iran and North Korea also would be a priority, Kerry said, and he proposed closing the loophole in the Nuclear Nonproliferation Treaty (search) that allows those countries and others to use civilian nuclear power programs as cover for weapons development.

Toughening export controls, stiffening penalties and strengthening law enforcement and intelligence sharing would help the United States prevent trafficking in bomb-making materials and components, Kerry said. He pledged to appoint a national coordinator to focus on securing nuclear weapons and materials around the world.

"We have to do everything we can to stop a nuclear weapon from ever reaching our shore -- and that mission begins far away," Kerry said. "We have to secure nuclear weapons and materials around the world so that searching the containers here at the Port of Palm Beach isn't our only line of defense, it is our last line of defense."

Both Kerry and Bush are underscoring the importance of Florida in the electoral politics of 2004 with frequent visits to the state. Kerry is making his 17th visit to Florida since he began campaigning for the presidency. Bush has visited the state 21 times since he was elected.

Bush campaign spokesman Steve Schmidt dismissed Kerry's plan as embracing objectives already laid out by the president. "His failure to accept the success of negotiations with Libya and his criticism of a multilateral approach to confront the threat from North Korea demonstrate that John Kerry can't help but play politics with national security," Schmidt said.

Ashton Carter, former assistant secretary of defense for international security policy in the Clinton administration, said Bush pursues nuclear supplies a bit at a time and country by country. Kerry would accelerate the process by getting rid of all supplies at once, Carter said in remarks on behalf of the Kerry campaign.

Kerry is delivering a series of speeches on national security during an 11-day tour that ends Sunday, the 60th anniversary of the Allied invasion at Normandy, France, during World War II.