Setting aside decades of acrimony over President Ronald Reagan’s vision of a “Star Wars” missile shield, the United States and Russia have been holding exploratory but serious talks about potential ways to cooperate on missile defense in Europe.

Russian and U.S. officials have met multiple times in Moscow and Washington since January to consider sharing data from sensors that could detect the launch of a ballistic missile from Iran or another hostile country.

Both sides have cautioned that no deal is imminent and that big differences remain. But the issue has been given a boost by back-to-back visits to Russia this month by Vice President Biden and Defense Secretary Robert M. Gates.

“We’ve disagreed before, and Russia still has uncertainties,” Gates said Monday in a speech to Russian naval officers in St. Petersburg. “However, we’ve mutually committed to resolving these difficulties in order to develop a road map toward truly effective anti-ballistic missile collaboration.’’

Such an assessment marks a sharp turnaround from years of bitter contention over missile defense. Although Washington always has portrayed its missile defense plans as purely defensive in nature, Moscow has eyed them as a backdoor plot to neutralize Russia’s massive nuclear arsenal.

Mutual suspicions over missile defense nearly derailed the New START arms-control pact last year. Although the treaty was ultimately ratified, U.S. officials until recently were largely dismissive of the idea that there was room for cooperation with Russia on missile defense.

“There is no meeting of the minds on missile defense,” Gates told a Senate panel in June. “The Russians hate it. . . . They will always hate it, mostly because we’ll build it and they won’t.”

Russia registered a change of heart in December, however, when NATO voted at a summit in Lisbon to adopt missile defense as a shared mission and to endorse the Obama administration’s plan to build a shield in Europe.

Russia and NATO subsequently agreed to formal talks over missile defense to determine whether cooperation was possible. In Moscow, President Dmitry Medvedev later explained in a speech to his country that the alternative to collaborating with the United States and NATO on missile defense was “a new arms race,” which Russia could not afford.

Since then, U.S. diplomats and defense officials have been meeting regularly with their Russian counterparts. Although there is not a precise timetable for the talks, Russia and NATO are scheduled to report on their progress in June.

The United States and NATO have ruled out a full partnership on missile defense, making clear that Russia would continue to be solely responsible for the defense of its territory, and NATO for its own. The Obama administration has also said that the talks with the Russians will not constrain its plans for a missile shield in Europe or elsewhere.

“This cooperation can happen even as we have made clear that the system we intend to pursue with Russia will not be a joint system, and it will not in any way limit the United States’ or NATO’s missile defense capabilities,” James N. Miller, the Pentagon’s principal deputy undersecretary for policy, told a House panel this month.

One possibility is that Russia and the United States could establish a “data fusion center” in which they could share information from their respective radar installations, which could provide earlier or more detailed warnings of a pending ballistic missile attack.

The Obama administration has been careful not to overstate the potential for partnering with the Russians. But U.S. officials have become more cautiously optimistic since the start of the year.

“There is a potential for cooperation, and real cooperation,” John F. Plumb, the Pentagon’s principal director for nuclear and missile defense policy, said in an interview. “Of course, it’s difficult. This is not going to be easy. There’s a lot of history.”

In Russia, security analysts said the benefit to Moscow would be primarily political. While the United States is worried about Iran, they said, Russia is more concerned about being excluded from NATO planning in the long-term.

“This is a political project, first of all,” said Tatyana Parkhalina, director of the Center for European Security in Moscow. “In practice, it would mean the integration of the Russian military into Euro-Atlantic security. Russia has articulated several times that it is not currently integrated into the process of decision-making in Europe. This is a big headache for the Kremlin.”

The improved climate on missile defense cooperation is part of the Obama administration’s overall effort to “reset” relations with Moscow after they had deteriorated under President George W. Bush.

Russia was particularly riled by Bush’s plan to install a missile defense shield in Europe that would have included missile interceptors in Poland and a radar installation in the Czech Republic — much too close to the Russian border for Moscow’s comfort.

In September 2009, Obama announced that he was overhauling Bush’s plan for a European shield. Obama’s approach will rely more heavily on anti-ballistic missile radars and interceptors based on Navy ships in the Mediterranean Sea.

The new system, which is seen as less threatening by the Kremlin, will be phased in starting this year and is scheduled to become fully operational in 2020.

Special correspondent Will Englund in Moscow contributed to this report.