WASHINGTON — By removing a single word from legislation governing the military, Congress has laid the groundwork for both a major shift in U.S. nuclear-defense doctrine and a costly effort to field space-based weaponry.
Experts say the changes, approved by overwhelming majorities in the House and Senate, could aggravate tensions with Russia and China, and prompt a renewed nuclear arms race. The bill awaits action by President Barack Obama. The White House has not said what he will do.
For decades, America's defense against nuclear attack has rested on two objectives: The nation's homeland missile defense system is designed to thwart a small-scale, or "limited," attack by the likes of North Korea or Iran. As for the threat of a large-scale strike by China or Russia, the prospect of U.S. retaliation is supposed to deter both from launching missiles.
Central to this strategy was a one-word qualifier — "limited" — used to define the mission of the homeland defense system. The language was carefully crafted to avoid reigniting an arms race among the superpowers.
Now, with virtually no public debate, bipartisan majorities in Congress have voted to remove the word "limited" from the nation's missile defense policy. They did so in giving final approval to the year-end defense bill, the National Defense Authorization Act.
A related provision of the law calls for the Pentagon to start "research, development, test and evaluation" of space-based systems for missile defense.
A space-based defense program would hinge on annual congressional appropriations and decisions by the incoming Trump administration.
Defense scientists said the idea that a space-based system could provide security against nuclear attack is a fantasy.
"It defies the laws of physics and is not based on science of any kind," said L. David Montague, a retired president of missile systems for Lockheed, and co-chair of a National Academy of Sciences panel that studied missile defense technologies at the request of Congress.
"Even if we darken the sky with hundreds or thousands of satellites and interceptors, there's no way to ensure against a dedicated attack," Montague said. "So it's an opportunity to waste a prodigious amount of money."
He called the provisions passed by Congress "insanity, pure and simple."
The National Academy study, released in 2012, concluded that even a bare-bones space-based missile defense system would cost about $200 billion to put in place, and hundreds of billions to operate in subsequent years.
Rep. Trent Franks, R-Ariz., who introduced and shepherded the amendments in the House, when asked whether the nation could afford it, replied: "What is national security worth? It's priceless."
Philip E. Coyle III, a former assistant defense secretary who headed the Pentagon office responsible for testing and evaluating weapon systems, described the notion of a space-based nuclear shield as "a sham."
"To do this would cost just gazillions and gazillions," Coyle said. "The technology isn't at hand — nor is the money. It's unfortunate from my point of view that the Congress doesn't see that.
"Both Russia and China will use it as an excuse to do something that they want to do."
The word "limited" has guided U.S. policy since the National Missile Defense Act of 1999. The qualifier reflects, in part, the reality that intercepting and destroying incoming warheads is supremely difficult, and that it would be impractical to field enough interceptors to counter a large-scale attack. Any such system, by its very nature, would be limited.
The current homeland anti-missile system — the Ground-based Midcourse Defense system, or GMD — relies on interceptors at Vandenberg Air Force Base in California and Fort Greely, Alaska. In flight tests, the system, which has cost more than $40 billion, has managed to destroy mock enemy warheads only about half the time.
Military officials estimate that, in the event of an attack, the U.S. would have to fire four or five interceptors for every incoming warhead. As a result, the system's arsenal of 34 operational interceptors could be rapidly depleted.
The 1999 law "threaded the needle between defending against a potential North Korean or Iranian threat and not rocking the boat too much with Russia and China," said Laura Grego, a physicist who led a recent study of GMD for the Union of Concerned Scientists.
"So just trashing that without a real substantive discussion is, I think, shameful," Grego said.
Franks said in an interview that he drew inspiration from President Ronald Reagan's Strategic Defense Initiative of the 1980s, which was intended to use lasers and other space-based weaponry to render nuclear weapons "impotent and obsolete." Known as "Star Wars," the initiative cost $30 billion, but no system was ever deployed.
Franks said that by striking the word "limited" from the homeland defense system's mission, and at the same time pursuing a space-based system, the U.S. is on a path to better safeguard its security. He said the new approach would protect both U.S. territory and surveillance satellites.
"I hope that the day will come when we could have solid-state lasers in space that can defeat any missile attack," Franks said "That day is a long ways off. But fortunately, it's a little closer, and a little more certain, with the passage of these amendments."
The new policy he championed says America "should maintain and improve a robust layered missile defense system capable of defending the territory of the United States and its allies against the developing and increasingly complex ballistic missile threat."
Franks suggested that Americans have no reason to fear a space-based arms race with China or Russia. He also said he had been surprised by the absence of Democratic opposition to his proposals.
The first of his amendments — to eliminate "limited" from U.S. policy — was approved in April by the House Armed Services Committee with no debate and without a recorded roll-call vote.
At a committee hearing May 17, a senior Democrat on the committee, Rep. Jim Cooper of Tennessee, offered mild protest.
"I think it was a mistake to mandate a poorly thought out, unaffordable and unrealistic missile defense policy, including plans for a space-based missile deterrent," Cooper said.
But neither Cooper nor any other House Democrat sought to overturn the provisions, and he was among those who voted to pass the overall bill the next day.
"I'm a little stunned that we didn't get more profile on it," Franks said. "That's fine with me, because that may have made my job easier."
Franks' Republican partner on the legislation, Sen. Ted Cruz of Texas, enjoyed a similarly smooth path.
Deliberations of the Senate Armed Services Committee were closed, forestalling public debate.
The legislation was approved by a roll call vote of 16-10, with two Democrats, Sens. Joe Manchin III of West Virginia and Tim Kaine of Virginia, the party's eventual vice presidential nominee, joining the Republican majority.
In June, Sen. Edward J. Markey, D-Mass., sought to restore "limited," saying that the change in U.S. policy would create "the impetus for a new arms race" with Russia and China. Markey offered an amendment on the Senate floor but could not muster enough support to bring it to vote.
The same month, the Obama administration criticized the changes in the Senate bill, saying it "strongly objects" to removing "limited" and to placing anti-missile weaponry in space. The statement stopped short of threatening a veto.
The policy changes met opposition from another quarter as well. At a congressional hearing in April, Franks pressed Vice Adm. James D. Syring, director of the Missile Defense Agency, for his stance on expanding U.S. capability into space.
Syring pushed back.
"I have serious concerns about the technical feasibility of the interceptors in space and I have serious concerns about the long-term affordability of a program like that," he said.