HUNTSVILLE, Ala. — Twenty years after President Ronald Reagan created an international furor by proposing to place weapons in space, the Pentagon has put nearly every major element of the original program back in the center of its plans as part of a national missile shield.
Unlike the ground-launched interceptor that successfully pulverized a mock warhead above Earth's atmosphere a week ago, space-based defenses would be placed in orbit as permanent sentinels, waiting until an enemy warhead rose above the atmosphere before trying to obliterate the warhead, the missile carrying it or both.
Along with intensified work on the ground-based system, the Pentagon's new plan calls for the accelerated development of chemical lasers that would fly in space or high in the atmosphere, fresh research on an abandoned program to launch thousands of interceptors into space, and the expansion of a project to place dozens of sensor-laden satellites into orbit.
But even some experts who support research on missile-defense systems have reservations about the new initiatives.
"We've now gone back to the SDI era of the first Reagan administration," said Stephen I. Schwartz, publisher of the Bulletin of the Atomic Scientists. "It's clearly their intention to put weapons in space to both defend U.S. assets as well as attack enemy missiles and enemy satellites."
Backers of the space shield, which military officials described in detail during a three-day briefing on missile defense here recently, say it would be a crucial part of the Bush administration's plans for a layered defense that would take multiple shots at a missile during various phases of its flight.
The shield, the officials said, would theoretically allow for 24-hour coverage of the globe, including the chance of knocking down missiles while they are still boosting — and therefore highly vulnerable — without having to station equipment near the launching site.
In a swift reawakening of the controversies generated by Reagan's program, critics of the plan fear that it could transform space into a potential battlefield.
In this view, American weaponry in space would force other nations to counter with anti-satellite weapons of their own, leading to an arms race in space. Looming over all those worries are doubts that the proposed technology could actually function as designed and provide an effective shield.
"Even developing and testing these space-based technologies is dangerous because it forces our adversaries to do the same thing," said Tom Z. Collina, director of the global security program at the Union of Concerned Scientists. Despite criticisms that the Pentagon was bringing back Star Wars, Lt. Col. Rick Lehner, a spokesman for the Ballistic Missile Defense Organization, said the aim was simply to determine whether worthwhile ideas from the old Strategic Defense Initiative Organization had been abandoned too soon.
"What we wanted to do was to go back and look at all of the technology that was developed since the beginning of the SDIO," Lehner said, in order to "see whether any of this technology would be applicable to a missile-defense system now."