The Pentagon seems poised to announce on Thursday an end to a missile defense program that until now had infuriated Russians and piqued concern among Eastern Europeans.

The decision — one Pentagon officials said "had nothing to do with Russia" — is still likely to curry favor within Moscow, which attributed a recent thawing of relations with the United States in part to the proposed missile defense shield.

"We will announce that we are making a major adjustment to our European missile defense system that is designed to protect our forces and our friends in Europe from the growing Iranian short- and medium-term missile threat," Geoff Morrell, the Pentagon's press secretary, told reporters Thursday morning.

First envisioned by the Bush administration, the missile defense program would have placed interceptors in Poland and a radar station in the Czech Republic to stave off any nuclear threat posed by Iran. Then-Russian President Vladmir Putin, however, was a chief opponent of the idea, insisting at the time that the United States's proposed shield was little more than regional politicking too close to his state's borders.

The standoff between the two nuclear powers continued for months, perhaps peaking in November when Russian leaders threatened to position their own missiles within reach of Poland if the United States constructed the shield. But the Bush administration remained steadfast in its support for the program, and the policy remained relatively unchanged.

The Obama administration's stance, however, will hardly appease all parties. Foremost among the unsatisfied are likely to be Republicans, who have long supported the missile shield. Across the ocean, some Eastern European leaders, too, fretted the White House's new call.

But the Pentagon insisted Thursday morning that its decision was purely a tactical move to better manage an Iranian threat — not necessarily a political maneuver to appeal to any one, concerned foreign power.

"This improvement to the system has nothing to do with Russia and everything to do with Iran," Morrell said, adding that "intelligence shows [the Iranians] are much more fixated on developing capable short- and medium-range missiles."