After the tensions over Kosovo's declaration of independence, it is clear "that we have reached the limit in foreign policy in relations with Russia," Steinmeier told German regional daily Leipziger Volkszeitung.
The United States wants to see former Soviet republics Georgia and Ukraine given a Membership Action Plan (MAP) - a formal step to joining NATO - at the summit in Bucharest running through Friday.
The issue has vexed Russia, with incoming president Dmitry Medvedev last week saying that the prospect of NATO coming closer to its borders was "extremely troublesome."
Steinmeier stressed that German opposition to Georgia and Ukraine joining NATO was not because of Russian objections to such a move, however. Steinmeier said he did not want to "be accused of playing the Russia card when it comes to the NATO membership of Georgia and Ukraine." But he added that there was "this year no convincing reason ... to create more tension," Steinmeier said.
German Chancellor Angela Merkel signalled early this month that she opposed Georgia and Ukraine joining, saying the alliance should wait until the people of the two countries back membership and the region becomes more stable. A number of NATO's 26 other members including France also have misgivings.
Kosovo's declaration of independence from Serbia earlier this year added to strains in the West's relations with Russia, with Moscow supporting Belgrade's opposition to the move but many Western powers recognizing the new country.