His remarks in an interview with Larry King were more pointed than those of President Dmitry Medvedev the day before. Medvdev had warned in vaguer language that a failure to reach an agreement on nuclear weapons will inevitably lead to a new arms race. But Putin tied a nuclear buildup to the fate of the missile defense system, saying that the United States needs to accept Russia's proposals on the joint effort.  "If our proposals will be met with negative answers ... Russia will have to ensure her own security through different means," he said.  "This is not a threat," Putin said. "We've been simply saying that this is what all of us expects to happen if we don't agree on a joint effort there."  Putin said that if the missile defense system excludes Russia and includes installations along Russia's borders, Moscow will see that as a threat and be forced to respond with an expansion and updating of its own weapons systems.  Medvedev met with NATO leaders in Lisbon on Nov. 20 and endorsed a joint approach.  A potential obstacle, though, could arise if the U.S. Senate fails to ratify the New START treaty limiting nuclear arms. The treaty would further reduce the nuclear arsenals of the United States and Russia, though not drastically, and it would allow mutual inspections to resume. The Obama administration has been pushing hard for Senate ratification during the lame duck session, but some Republicans have called for a delay. The original START weapons treaty, which went into effect in 1994, expired a year ago.  Russians understand that the treaty has been caught up in domestic American politics, said Irina Kobrinskaya, an analyst with Institute of World Economy and International Relations for the Russian Academy of Sciences. But a failure by the Senate to ratify it would strengthen the hand of conservatives within the military establishment in Moscow who are wary of Medvedev's warmer relations with Washington.  In the interview, to be broadcast Wednesday evening, Putin also said he would make a decision next year about whether to run again for the presidency, a post he held from 2000 to 2008. He reacted angrily to the disclosure, in the WikiLeaks document dump, that American diplomats had called him Batman to Medvedev's Robin.  "The truth of the matter is, this is about our interaction, which is an important factor of the domestic policies in this country," he said. "But to be honest with you, we didn't suspect that this would be done with such arrogance, with such a push and, you know, being so unethically done."  But Putin also suggested that the WikiLeaks documents may be fabrications.  Staff writer Kathy Lally contributed to this article.
MOSCOW--Russia will have to expand and update its nuclear arsenal if it can't reach an agreement with NATO on a new missile defense system, Prime Minister Vladimir V. Putin said in an interview to be broadcast Wednesday on CNN.