"I have concluded the ABM treaty hinders our government's ability to develop ways to protect our people from future terrorist or rogue-state missile attacks," Mr. Bush said Thursday morning from the White House.
Russian President Vladimir Putin called the U.S. decision to withdraw from the ABM treaty a "mistake."
In a nationwide television address, Putin said Mr. Bush's announcement was not a surprise for Moscow. Putin repeated Russia's often-stated position that the treaty is a cornerstone of world security.
However, Secretary of State Colin Powell said Thursday that Putin had proposed slashing his nuclear arsenal to a range of 1,500 to 2,200 warheads in response to a proposal by President Bush to make similar cuts over 10 years.
The U.S. and Russia announced last Wednesday that they had slashed their nuclear stockpiles to below the level of 6,000 warheads set by the START-1 treaty signed in 1991.
"President Putin has now responded to President Bush's Washington-Crawford statement of reducing our strategic offensive inventory down to a range of 1,700 to 2,200 operationally deployed warheads," Powell said.
"President Putin has now indicated that he would like to go to a range of 1,500 to 2,200, so we're in the same range," he told a news conference.
Powell was speaking after Bush announced America's intention to withdraw in six months from the ABM Treaty.
Mr. Bush made the announcement in thRose Garden with Secretary Powell, Defense Secretary Donald Rumsfeld, Joint Chiefs Chairman Gen. Richard Myers and national security adviser Condoleezza Rice at his side.
"We're moving to replace mutually assured destruction with mutual cooperation," Mr. Bush said.
The U.S. ambassador to Moscow delivered formal notice of the presidential decision to Russian officials at 4:30 a.m. EST, according to a senior administration official who spoke on condition of anonymity.
The brief legal document invokes Article 15 of the 29-year-old treaty to give Russia six months' notice. The official said Mr. Bush has, in effect, pulled out of the treaty with the notification, though the United States cannot conduct missile tests barred by the treaty for six months.
At 9 a.m. EST, formal notice was given to Ukraine, Kazakstan and Belarus, former Soviet states that signed memoranda of understanding tying them to the pact under the Clinton administration.
Russian Prime Minister Mikhail Kasyanov said the decision was regrettable because it undermined global strategic balances but he was not concerned about Russia's security.
"Russia can be unconcerned with its defense systems," said Kasyanov, who was in Brazil for a two-day visit. "Maybe other nations should be concerned if the United States chooses to abandon the Anti-Ballistic Missile Treaty."
"Today, the events of Sept. 11 made all too clear the greatest threats to both our countries come not from each other or other big powers in the world but from terrorist attacks who strike without warning or rogue states who seek weapons of mass destruction," Mr. Bush said.
Putin cautioned last winter that jettisoning the treaty could lead to the unraveling of three decades of arms control accords. China has warned a new arms race could ensue.
Mr. Bush had tried to strike a deal with Putin that would allow the United States to move to a new phase of testing in the U.S. missile defense program. Putin had sought authority to sign off on U.S. missile tests, but the request was rejected, administration officials said.
The next scheduled step is the beginning of construction next spring of silos and a testing command center near Fairbanks, Alaska.
The Bush administration intends to cooperate with Russia at least to the extent of informing Moscow of steps being taken to advance the missile-shield program.
That's not likely to stop Russia from taking retaliatory steps. A senior Russian lawmaker predicted Russia will pull out of the Start I and Start II arms reduction treaties.
"We believe that offensive and defensive tools of nuclear deterrence must be linked," said Dmitry Rogozin, chairman of the Duma's international affairs committee, according to Interfax news agency.
Such a spiral of withdrawals would be dangerous and predictable, said Sen. Carl Levin, D-Mich., chairman of the Senate Armed Services Committee.
"Unilateral withdrawal will likely lead to an action-reaction cycle in offensive and defensive technologies, including countermeasures," he said. "That kind of arms race would not make us more secure."
Sen. Joseph Biden, D-Del., chairman of the Senate Foreign Relations Committee, also said quitting the treaty could lead to a new arms race.
"About eight months ago they were taking about weaponizing space," Biden said Wednesday. "God help us when that moment cmes."
The ABM treaty is based on the proposition that stripping a nuclear power of a tough missile defense would inhibit it from launching an attack because the retaliation would be deadly.
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