Such a statement may sound puzzling in an age of "dirty" bombs and other terrorist threats, but it's true.

That's because the United States now has officially withdrawn from the Anti-Ballistic Missile (ABM) Treaty, a pact we signed in 1972 with the former Soviet Union. As a result, we no longer face the treaty's roadblocks to creating a missile defense that can shield the American people, our armed forces and our allies from the ultimate weapon: long-range ballistic missiles.

With the treaty gone, the engineers and scientists who work on missile defense finally can do something they've been barred from doing for three decades-innovate.

The ABM Treaty always was a Luddite solution to the nuclear arms race, because it severely limited not only the use of a missile-defense system, but the development and testing of one as well. Indeed, its terms were broad enough that treaty supporters used it in recent years to impose restrictions on anti-missile systems that didn't even exist in 1972.

The treaty's demise, however, opens a wide range of opportunities to American scientists and engineers. Here are just some of the things they can do in the near future that will help us deploy a working missile defense:

• Use sea-based radar to support interceptor tests against long-range target missiles. ABM Treaty provisions forced Defense Secretary Donald Rumsfeld to exclude the use of sea-based radar-which, being mobile, is less vulnerable to attack-to monitor recent missile-defense tests. Sources say the next test of that system, scheduled for July, will indeed employ sea-based radar.
• Test a mobile, land-based interceptor against a missile that can fly faster than 3.2 miles per second or farther than 2,170 miles (roughly the distance from New York to El Paso, Texas). The Pentagon couldn't test an interceptor that flew this fast or this far before for the same reason that it couldn't use sea-based radar: The ABM Treaty wouldn't allow it.
• Test space-based interceptors against a ballistic missile of any range. This is where supporters of the ABM Treaty took their most extreme position. All agreed that the treaty permitted land- and sea-based defenses against short-range missiles. But ABM defenders objected to any kind of a space-based missile defense, claiming that it could be converted too easily to a system capable of defending against long-range missiles. A national defense system sounds pretty good to most of us. But it's something the treaty specifically prohibited.
• Use the Navy's "extended air defense" system. Last year, the Navy said it could counter North Korean missiles in the event of an emergency. The plan called for modifying two Aegis-class ships and stationing them near Japan. The modified ships then could shoot down attacking missiles in the early, or "boost" phase of flight, when they're traveling more slowly and can be more easily tracked and destroyed. This "extended air defense" would take 12 to 18 months to get ready and would cost between $150 million and $200 million-a cheap price to pay.
  

There are many other options, of course, and the list of what we can do surely will lengthen considerably now that we've shed the ABM straitjacket. But a note of caution: After 30 years of being told what not to do with missile defense, scientists and engineers may be tempted to experiment with every option under the sun.

That temptation must be resisted. We need to remain focused. Our missile-defense program already is lagging behind the threat. (It's been four years since North Korea tested its first long-range missile.) There's an immediate need to get at least a limited missile defense in the field.

America must concentrate on the options that offer fast deployments and make these systems effective as quickly as possible. Our adversaries aren't sitting still-and neither should we.

Baker Spring is the F.M. Kirby Fellow in National Security Policy at The Heritage Foundation (www.heritage.org), a Washington-base public policy institute.