BERLIN  The deep concern among America’s Eastern European allies over improved relations between Russia and the United States spilled into the open on Thursday when 22 prominent figures, including Poland’s Lech Walesa and the Czech Republic’s Vaclav Havel, published an open letter to the Obama administration begging not to be forgotten.

In the letter, the leaders urged President Obama and his top policy makers to remember their interests as they negotiate with Russia and review plans for missile defense bases in Poland and the Czech Republic. Abandoning the missile defense plan or giving Russia too big a role in it could “undermine the credibility of the United States across the whole region,” the letter said.

The letter was published on the Web site of the Polish newspaper Gazeta Wyborcza and was signed by former presidents, like Mr. Walesa and Mr. Havel, as well as other former heads of state, top diplomats and intellectuals from a broad range of countries, including Hungary, Bulgaria and Estonia.

“Our region is one part of the world that Americans have largely stopped worrying about,” the letter said, even though “all is not well either in our region or in the trans-Atlantic relationship.”