President Bush has signed a defense bill that provides close to $8-billion for development of a controversial missile defense program. U.S. intelligence experts say that when it comes to delivering weapons of mass destruction, ships, planes and trucks pose a greater threat than missiles.

An unclassified report released this week by the Central Intelligence Agency acknowledges ships, airplanes and trucks are not as prestigious or useful as tools of deterrence and diplomacy as intercontinental ballistic missiles.

But the report says the U.S. intelligence community believes that American territory is more likely to be attacked with chemical, biological, radiological or nuclear weapons delivered by such conventional means than by missiles.

It cites several reasons for the assessment, calling non-missile delivery systems cheaper than long-range missiles, it says they are more easily concealed, and they are probably more reliable and accurate.

In addition, the report says ships, airplanes and trucks will be able to avoid U.S. missile defenses.

The assessment is tucked away at the end of a National Intelligence Estimate titled Foreign Missile Developments and the Ballistic Missile Threat through the year 2015.

It notes missile threats posed by North Korea, Iran and possibly Iraq in addition to the long-standing missile forces of Russia and China.

But it also warns terrorist groups have used, possessed or expressed an interest in chemical, biological, radiological and nuclear weapons.

And it says most such groups have not only threatened the United States but all of them have the ability to attack the country without using missiles.