WASHINGTON – Polish Prime Minister Donald Tusk said President Bush yesterday had removed key stumbling blocks in negotiations to allow U.S. missile defense interceptors on Polish soil.

Negotiations had stalled over Poland’s demand for help in upgrading its military in exchange for allowing the interceptors. U.S. negotiators wanted to deal with the Polish demands separately and leave promises vague.

But Tusk said Bush had agreed that the missile defense program and the U.S.-aided modernization of the Polish military would be considered all in “one package.”

“The words of President Bush were very convincing,” he told The Associated Press minutes after leaving the White House. “This is a politician who is controversial for some but in my opinion is very trustworthy.”

Bush, in a joint appearance with Tusk at the White House, said he had assured the prime minister that the United States would develop a concrete plan for helping Poland modernize its military “before my watch is over.”

The Bush administration has been seeking to begin construction of its European missile shield while it is still in office and to complete it by 2012. The plan also includes installing radar in the Czech Republic. But because the negotiations with Poland are lagging and any deals would have to be approved by the Polish and Czech parliaments, it may be difficult to meet the timetable.

Polish supporters of the plans are concerned that a new U.S. administration could kill the project. Among the major candidates to succeed Bush, Republican John McCain is a strong supporter of the missile defense program, while Democrats Barack Obama and Hillary Rodham Clinton have been less vocal.

The missile defense plans have become one of the thorniest issues in U.S.-Russian relations. Russia opposes the U.S. plan to build part of its global missile defense system so close to Russian borders, arguing that it would undermine the Russian deterrent. The Polish government argues that the security backing is necessary because Russia has threatened to target Poland with nuclear missiles if it should allow the interceptors.

Tusk said Bush had assured him that the United States would continue to try to convince Russia that the missile shield was not a threat. The United States says it is aimed at countering threats from countries such as Iran and North Korea.

The White House denied the suggestion that the military help is a reward for Polish agreement on the interceptors or that it is needed because of a Russian threat to Poland.

“It is certainly not a quid pro quo,” White House press secretary Dana Perino said. “Who is suggesting that Russia is going to attack anybody?”

When told that Polish officials said this, Perino said it was not part of the discussions yesterday between Tusk and Bush.

Tusk said the United States had backed down from an insistence that it would need six months to consider how it could help Poland upgrade its military. He said Secretary of State Condoleezza Rice told him Monday that the period could be reduced to three months.