Washington  - Barack Obama Wednesday charged that the Bush administration has failed to confront the threat of nuclear terrorism and vowed that if elected president, he would lead the effort to corral errant nuclear materials and stay one step ahead of biological and cyber threats.

Obama, the presumptive Democratic nominee for president, aimed to bolster his credentials on national security with the gathering organized by his campaign - billed as a summit on 21st Century threats at Purdue University in Indiana.

While Obama is seen as strong on major domestic issues such as health care and the economy, polls show the electorate believes Republican Senator John McCain, a downed Navy pilot in Vietnam, is stronger on security and military issues.

Obama called nuclear terrorism "the gravest danger we face." He called President George W Bush to task for spending nearly 1 trillion dollars on the war in Iraq, which had no active nuclear programme, while 50 tons of highly enriched uranium at civilian nuclear facilities around the world often is "poorly secured."

"Now, we worry - most of all - about a rogue state or nuclear scientist transferring the world's deadliest weapons to the world's most dangerous people: terrorists who won't think twice about killing themselves and hundreds of thousands in Tel Aviv or Moscow, in London or New York," Obama said.

Obama vowed to "lead a global effort to secure all loose nuclear materials around the world" during his first term as president, to further negotiate with Russia to achieve "deep reductions" in global nuclear arsenals and to pressure the US Senate to ratify the Comprehensive Test Ban Treaty.

Obama charged that the nuclear, biological and cyber threats of the 21st century "have been neglected for the last eight years" under Bush.

The Bush administration can point to some successes, including its role in securing Libya's 2003 agreement to dismantle its nuclear weapons and North Korea's recent overtures to follow suit. The White House has kept up steady pressure for years to get Iran to dismantle its uranium enrichment programme.

Under Bush, the US has supported efforts to denuclearize former Soviet states, and the president also launched the Proliferation Security Initiative, an international agreement to cooperate in the interdiction of illicit transfers of missile and weapons of mass destruction technology.

Obama also spoke of the threat from bio-terrorism, saying he would launch a government-wide effort and a partnership to invest 5 billion dollars over three years to forge an international effort to "interdict dangerous bio-weapons" around the world.

The vulnerability of computer information networks that are the "backbone" of the economy, national security and "our personal well- being" would become a top priority for Obama as president.

"I'll declare our cyber-infrastructure a strategic asset, and appoint a national cyber advisor who will report directly to me," Obama said.

The Indiana "summit" on security included top experts on nuclear non-proliferation, bioterrorism and cyber security such as former Democratic Senator Sam Nunn, who heads the nonprofit Nuclear Threat Initiative, and has been mentioned as a possible vice presidential candidate. (dpa)