The plan has upset some loyal allies with its appeal to Russia. Yet if the new approach pans out, using more diverse defenses and greater diplomatic leverage, it could provide protection from Iran not only for Europe but also Israel and Arab states in the Persian Gulf who fear the Iranians' pursuit of ballistic missiles and nuclear weapons.
With U.S. troops already stationed on Iran's eastern and western flanks - in Iraq and Afghanistan - the addition of anti-missile weapons aboard U.S. Navy ships in the region would add to Iran's military isolation. And the hope is that it would ease Israel's sense of urgency for taking military action against Iran.
Critics say the emerging Obama approach does too little to enhance protection of the U.S. homeland from missile threats while putting too much stock in intelligence estimates of Iran's missile plans.
On the diplomatic front, President Barack Obama hopes Russia will find more reason to go along with U.S. efforts to stop Iran from building a nuclear bomb, now that Washington has abandoned a Bush administration approach to missile defense in Europe that Moscow viewed as a threat to its own security.
In a new outreach to Russia on Friday, the civilian chief of NATO called for the U.S., Russia and NATO to link their missile defense systems against potential new nuclear threats from Asia and the Middle East. Previous such appeals for collaboration have produced little concrete result, but with Obama's change of approach this one may stand a better chance.
Russia publicly opposes any Iranian effort to develop nuclear weapons, but it also is against imposing new sanctions on Tehran. In the U.S. view, the threat of further sanctions is a necessary diplomatic tool.
Iran's nuclear ambitions are expected to be a central focus at a gathering of world leaders at U.N. headquarters in New York next week. And U.S, Russian and other powers are to sit down with Iranian officials on Oct. 1 for a resumption of talks on the nuclear issue as well as other security topics.
Britain's ambassador to Washington, Nigel Sheinwald, told The Associated Press on Friday that he considered it encouraging that Russia quickly welcomed Obama's decision to change course in Europe.
"One way or the other, it cannot but contribute positively to the objectives of the reset of relations with Russia," Sheinwald said, adding that "we do want Russia to be an active and committed participant in these discussions on Iran."
Ray Takeyh, an analyst at the Council on Foreign Relations who served as a State Department adviser on Iran policy until last month, said Obama's blueprint for missile defense in Europe evokes an idea raised in July by Secretary of State Hillary Rodham Clinton for a defense umbrella over the Persian Gulf.
"Logically, there is a connection there," Takeyh said in a telephone interview.
Defense Secretary Robert Gates made a similar link when he laid out details of the Obama plan for Europe.
"I don't want to get into it in too much detail," Gates told reporters Thursday, "but the reality is we are working both on a bilateral and a multilateral basis in the Gulf to establish the same kind of regional missile defense that would protect our facilities out there as well as our friends and allies."
The U.S. already is taking a similar approach in Asia, where sea-borne anti-missile weapons and mobile radars are arrayed to protect Japan and other allies from the threat of a North Korean missile strike.
Under the Obama plan for Europe, U.S. Navy ships equipped with anti-missile weapons would form a front line of defense in the eastern Mediterranean, combined with existing land-based anti-missile systems such as the Patriot ashore in Europe. A similar arrangement is foreseen for the Persian Gulf to protect not only U.S. ships that regularly patrol the Gulf but also Arab allies such as Saudi Arabia and Kuwait.
Clinton said in a speech at the Brookings Institution on Friday that the retooled approach to missile defense in Europe is mainly a response to a perceived change in Iran's ballistic missile priorities. The U.S. believes Iran is accelerating its short- and medium-range missile development and going more slowly than previously anticipated in building the long-range missile that once was the central threat.
"We believe we will be in a far stronger position to deal with that threat and to do so with technology that works and with a higher degree of confidence that what we pledge to do we can actually deliver," Clinton said.
She dismissed claims by critics that the administration changed course in order to placate the Russians and that the shift amounted to undermining NATO allies Poland and the Czech Republic, whose governments had agreed during the Bush administration to host key elements of the now-abandoned system.
"This decision was not about Russia. It was about Iran and the threat that its ballistic missile program poses," Clinton said.
At the Pentagon on Friday, Czech Defense Minister Martin Bartak, speaking through an interpreter, asserted that "missile defense doesn't end here." He said his country will evaluate the new plan and "we are going to figure out ways the Czech Republic can be involved in the future missile defense."
With Bartak at his side, Gates spoke optimistically of entering a new phase of cooperation with Russia.
"For more than two years I have encouraged the Russians that we are partners in this missile defense," Gates told reporters. "The Russians have a radar in southern Russia, the Armavir radar, that actually would fill a gap in coverage, and we would welcome the Russians networking with us in this. We think that we can make that happen."
Combined with the prospect of Iran building a nuclear weapon, the Iranians' missile program is a particularly urgent problem for Israel. In Tehran on Friday, Iranian President Mahmoud Ahmadinejad, who denies Israel's right to exist, lashed out at the Jewish state and again questioned whether the Holocaust happened.
Although Israel is not officially part of the U.S. missile defense system in Europe, Gates reiterated on Thursday that Washington is intent on helping Israel improve its defenses against an Iranian threat.