When President Obama got on the telephone with President Dmitri A. Medvedev of Russia last month, he was under the impression that they were finally close to wrapping up a long-delayed arms control treaty that he had originally expected to sign in December.

But to Mr. Obama’s surprise, Mr. Medvedev was not ready to sign off on a deal and raised issues that required more discussion, American officials said. As he hung up, the officials said, a frustrated Mr. Obama realized that the two sides were not as close as he had thought and sent negotiators back to the table.

The fitful effort to fashion a treaty that would be a signature achievement of his presidency has demonstrated the hurdles Mr. Obama faces in his drive to reset relations with Russia after years of tension.

When President Obama got on the telephone with President Dmitri A. Medvedev of Russia last month, he was under the impression that they were finally close to wrapping up a long-delayed arms control treaty that he had originally expected to sign in December.

But to Mr. Obama’s surprise, Mr. Medvedev was not ready to sign off on a deal and raised issues that required more discussion, American officials said. As he hung up, the officials said, a frustrated Mr. Obama realized that the two sides were not as close as he had thought and sent negotiators back to the table.

The fitful effort to fashion a treaty that would be a signature achievement of his presidency has demonstrated the hurdles Mr. Obama faces in his drive to reset relations with Russia after years of tension.

Russian Finance Minister Alexei Kudrin said the dollar is in “good shape,” further affirming that there’s no substitute for the world’s reserve currency.