The world faces an estimated 50 percent chance of a nuclear, biological, chemical or radiological attack over the next five years, according to national security analysts surveyed for a congressional study released Wednesday.

Using a poll of 85 nonproliferation and national security experts, the report also estimated the risk of attack by weapons of mass destruction at as high as 70 percent over the coming decade.

The Senate Foreign Relations Committee surveyed analysts around the world in late 2004 and early this year to determine what they thought was the threat posed by weapons of mass destruction.

The study was commissioned by committee Chairman Sen. Richard Lugar, R-Ind., whose nonproliferation (search) efforts in Congress have been credited with helping the states of the former Soviet Union lessen their stockpiles of nuclear, chemical and biological weapons.

"The bottom line is this: For the foreseeable future, the United States and other nations will face an existential threat from the intersection of terrorism and weapons of mass destruction," Lugar said in a statement.

Committee aides sent out surveys asking respondents the percentage probability that a biological, chemical, nuclear and radiological attack would occur over the next five and 10 years.

"If one compounds these answers, the odds of some type of WMD attack occurring during the next decade are extremely high," the report said, using the acronym for weapons of mass destruction.

The study said the risks of biological or chemical attacks were comparable to or slightly higher than the risk of a nuclear attack. However, the study found a "significantly higher" risk of a radiological attack.

It also said:

—Three-fourths of those surveyed said one or two new countries would acquire nuclear weapons during the next five years, and as many as five new countries could have such weapons over the next 10 years.

—Four-fifths of those surveyed said their country was not spending enough money on nonproliferation efforts.

—Survey respondents also agreed that terrorists — rather than governments — were more likely to carry out a nuclear attack.