The Russian government warned today that President Bush's intention to begin fielding a rudimentary antimissile system in 2004 meant that the plan had "moved into a new destabilizing phase."

The statement from the Russian Foreign Ministry indicated that although Russia has reluctantly accepted the inevitability of Washington's plans since Bush pulled out of the 1972 Anti-Ballistic Missile Treaty last year, it has yet to be reconciled to them. The Bush announcement, the statement said, was noted "with regret" in Moscow.

Russia has recently pressed to be incorporated into U.S. missile defense plans, however, arguing that joint missile defense is better suited to international realities than the unilateral program Bush is promoting.

Such cooperation, the Russian statement said, makes sense given the "fundamentally new relationship of strategic partnership" between the United States and Russia since the Sept. 11, 2001, terrorist attacks. "Moscow expects that the United States will give priority to implementation of this program of strategic partnership," the statement said, "and will involve its friends and partners in it rather than in a destabilizing race of strategic defensive arms."

Such words were a change from just a few years ago, when Moscow routinely warned that a major new arms race would be an inevitable outcome of a U.S. missile defense deployment, threatening global stability. Still, the Russians continued to bemoan the loss of the ABM Treaty, saying its absence could lead to "a new senseless arms race," as well as "diverting resources" from more pressing matters, such as the battle against international terrorism.

And Foreign Minister Igor Ivanov, speaking while en route to Washington to meet with Secretary of State Colin L. Powell, reiterated Moscow's opposition to deployment of a missile shield. "Such steps must not infringe on the security interests of Russia or other states," he said during a stopover in Tokyo. "Nor should they fuel an arms race."

Less measured comments came from the Kremlin, where presidential adviser Igor Sergeyev warned that Russia had received no guarantees that such a system would not be targeted against it.

"We cannot disregard the fact that elements of the U.S. missile defense system are being deployed in the north, not in the south, where the threat is coming from the so-called rogue countries," Sergeyev, a former Russian defense minister, told Interfax news agency.

He suggested that the destabilization caused by a U.S. missile defense system might contribute to spreading weapons of mass destruction. "In such a setting, it would be difficult to tighten control over the nonproliferation of weapons of mass destruction," he said.