Cohen told the Senate Foreign Relations Committee "the clock is ticking" for the United States to prevent "the Armageddon we all want to avoid."
Cohen's testimony -- his first in front of this committee since leaving his post at the Pentagon -- comes amid news reports that a top al Qaida lieutenant captured in Pakistan, Abu Zubaida, has told U.S. intelligence officials that the terror network has worked on creating a "dirty" nuclear bomb.
Such a bomb would use conventional explosives to spread radiation and terror.
Committee Chairman Joseph Biden, D-Del, said the United States must send money to Russia and give the administration more authority to work with the Russians and prevent nuclear materials from reaching terrorists' hands. Safety measures to stop terrorists from obtaining such materials are in serious disarray in Russia, Biden said.
According to Biden, Russia still has:
* Around 1,000 metric tons of excess highly enriched uranium, enough to produce 20,000 nuclear weapons.
* 160 metric tons of excess weapons grade plutonium.
* 40,000 metric tons of declared chemical weapons.
Russian experts in weapons of mass destruction face economic hardships that Cohen and senators of both parties said could lead them to sell their expertise to terrorists.
"There are many sources for weapons of mass destruction," Biden said. "But there is one place that has it all. That place is Russia."
Cohen said the reports about Zubaida show the United States must act aggressively to make sure terrorists do not get more potent tools, particularly from Russia. "I think it is, perhaps, the premier issue we have to address today," Cohen told the committee.
Senators from both parties said they would rush money to 10-year old programs set up between the United States and Russia to reduce such threats and would try to give the Bush administration more flexibility to spend it.
Sen. Richard Lugar, R-Ind., said terrorists would use such weapons if they could. "There is little doubt that Osama bin Laden and al Qaida would have used weapons of mass destruction on Sept. 11 if they had possessed them."