A National Missile Defense system is such a comforting thought that it is no wonder that presidents going back 30 years have an-nounced their intention to invest in a shield that will keep the nation safe from enemy missile attacks. But with numerous failures in its history, missile defense needs a thorough if not skeptical review by Congress before President Bush invests tax money yet again in this idea.

President Nixon had Safeguard, a missile defense system in North Dakota that was abandoned in 1976. President Reagan had the Space Defense Initiative, the space-based umbrella of protection that never made it off the ground. President Clinton had a ground-based system tested in the final year of his presidency that couldn’t tell a missile from a decoy. Now President Bush, without offering details, announced he too wants to spend tens of billions of dollars to provide this protection because “More nations have nuclear weapons and still more have nuclear aspirations.”

The estimated development cost of the president’s proposal is $60 billion to $100 billion, although without further details the cost is just as much a guess as the assumed ability to hit a missile with a missile. This cost must be balanced against other demands for government funding, including the other defense demands.

Vice President Dick Cheney, for instance, recently agreed with the common wisdom that terrorist attacks are a growing threat to the United States compared with missiles from rogue governments. (“I think we have to be more concerned than we ever have about so-called homeland defense, the vulnerability of our system to different kinds of attacks. … The threat of terrorist attack against the U.S., eventually, potentially, with weapons of mass destruction – bugs or gas, biological, or chemical agents, potentially even, someday, nuclear weapons,” the vice president said in The New Yorker.)

In his speech at the National Defense University earlier this week, President Bush properly addressed one of the risks of missile defense: that the United States could embark on it without the support or cooperation of other nations. The president had not only contacted world leaders before his speech to outline his program but repeatedly referred to consultations with “friends and allies.” The sketch the president presented Tuesday would include a defense shield not only for the United States but, apparently, much of the world.

This will not stop other nations from seeing the U.S. abrogation of the anti-ballistic missile treaty and the major increase in missile-defense spending as a reason or an excuse to build up their own nuclear weapons programs. It is a calculation Congress should be deeply involved in: How much is a missile defense worth if it immediately causes other nations to invest in technology to penetrate it?

President Bush was cautious in his ap-proach to this defense system, acknowledging that interim steps may be required and that any system must pass performance tests before undergoing full production. Congress’ role is to watch these developments closely, balance research investment in missile de-fense with opportunity elsewhere and, most importantly, gauge world reaction to ensure that a plan to increase security does not end up eroding it.