Czech officials also announced an agreement to install a missile tracking site for the system in their country.
NATO leaders were adopting a communique stating that "ballistic missile proliferation poses an increasing threat to allied forces, territory and populations." It also will recognize "the substantial contribution to the protection of allies ... to be provided by the U.S.-led system," senior American officials told The Associated Press on the condition of anonymity before the statement was released.
That was the message Washington had sought from the summit after it became clear that allies would not go as far as to take procurement decisions on a possible NATO add-on system to cover parts of southeast Europe not under its umbrella, Reuters reported.
The statement calls for NATO members to explore ways that the planned U.S. project, to be based in Poland and the Czech Republic, can be linked with future missile shields elsewhere. Leaders should come up with recommendations for NATO members to consider at next year's meeting, officials told the AP.
Significantly, the document also calls on Russia to drop its objections to the system and to accept U.S. and NATO offers to cooperate on building it, they said.
The plan calls for 10 interceptor missiles based in Poland and a tracking radar site in the Czech Republic.
At a news conference on the sidelines of the NATO summit in Bucharest, Romania, Czech Foreign Minister Karel Schwartzenberg announced that a deal with the U.S. would be signed in early May. No U.S. official was in attendance, but the Czechs distributed a joint U.S.-Czech statement that said, "This agreement is an important step in our efforts to protect our nations and our NATO allies from the growing threat posed by the proliferation of ballistic missiles and weapons of mass destruction."
The Poles have yet to agree to the plan.
The backing from NATO and the announcement with the Czechs provides Mr. Bush with a powerful leg up in his negotiations with Moscow over the issue.
Also on Thursday, leaders promised Ukraine and Georgia they would one day join NATO but rebuffed President Bush's demands to put the former Soviet republics on a path to membership immediately.
Germany, France and smaller NATO states rejected pressure at an alliance summit to offer the two countries a Membership Action Plan, a first step toward membership, saying neither was ready and such a move would risk provoking Russia.
But NATO leaders softened the blow by making a vague pledge to invite the two to join the alliance at some point in the future and saying former Cold War foe Moscow should have no influence on membership decisions.
"We agreed today that these countries will become members of NATO," NATO Secretary-General Jaap de Hoop Scheffer told a news conference.
"That is quite something," he added.
On other NATO enlargement decisions, Macedonia's U.S.-backed request for an invitation to join was blocked by Greece in a naming dispute, prompting Macedonian officials to storm out of the meeting, The New York Times reported.
Albania and Croatia secured invitations to join NATO and Bosnia and Montenegro were awarded closer ties.
"The unusually rancorous meeting of NATO members in Bucharest exposed sharp differences between nations, but despite the rancor President Bush won some agreement on bolstering the number of NATO troops in Afghanistan," The New York Times reported.
Also at the meeting, NATO countries reaffirmed a commitment to the mission in Afghanistan and Canada announced it will keep its troops in the country's restive south after NATO allies met its conditions by coming up with additional reinforcements, Prime Minister Stephen Harper said Thursday.
French President Nicolas Sarkozy also pledged an extra 700 soldiers for eastern Afghanistan, allowing the United States to say it would send an "equivalent" number to the south, the main front in the battle against Taliban insurgents.
