An artistic rendition of a space-based laser integrated flight experiment, which is part of the Star Wars missile defense system that President George W. Bush would like to see become a reality. Art Courtesy Global Network Web site at www.space4peace.org

Imagine if the United States could shoot down any missile rocketing toward our shores, making the country safe from nuclear attack.

That concept, known as a missile-defense shield, is getting a lot of attention by the Bush administration these days. The White House has asked Congress to increase the budget for research and development to $8.3 billion a year, up from $3 billion. One key component of the Bush administration plan is to deploy a ground-based system in Alaska that uses missiles to shoot down other incoming missiles.

To promote increased funding, the Bush administration reminds doubters that several countries could develop ballistic missiles capable of striking the U.S. Countries such as Iraq, Iran, and North Korea—dubbed the "Axis of Evil" by President Bush—are a much bigger nuclear threat than Russia.

"Today's most urgent threat stems not from thousands of ballistic missiles in the Soviet hands, but from a small number of missiles in the hands of these states, states for whom terror and blackmail are a way of life," President Bush says.

To some, the real threat could arrive in another way, such as suitcase bombs and biological agents. The high costs of missile defense have some wondering if the money might be better spent on other, more realistic, means of defense.

"We do not need a missile-defense system that could cost almost a half-trillion dollars," says Delaware Senator Joseph R. Biden, Chairman of the Foreign Relations Committee. "The real priorities of real people in real cities across America are far more earthbound and far less costly than missile defense."

Missile defense has suffered many setbacks over the years, including one in December. A test rocket had to be destroyed when it veered off course over the Pacific—an embarrassing mistrial for the administration.

The idea got its start in the 1980s under President Reagan, who, in 1983, called for the development of a system that would stop any nuclear attack. Dubbed the Strategic Defense Initiative, or SDI, the initiative was meant to be mostly based in outer space, using lasers and satellites. The media nicknamed SDI "Star Wars," a reference to the popular 1977 science-fiction film. About $50 billion was spent on SDI—which never came close to becoming a reality.

President Clinton canceled the program in 1993. A few years later, under the behest of a Republican Congress, Clinton agreed to a more modest deployment of a land-based system.