By Phil Stewart
MOSCOW (Reuters) - Defense Secretary Robert Gates arrived in Moscow on Tuesday for talks on Libya in the middle of the first major public spat between Kremlin chief Dmitry Medvedev and Prime Minister Vladimir Putin.
Gates will not meet Putin but will see President Medvedev, who rebuked his mentor on Monday for comparing the West's call for action in Libya to the crusades, the most public difference yet between Russia's ruling tandem ahead of 2012 elections.
On his flight to Russia, Gates praised strengthening ties with Moscow and noted that Russian leaders "despite their reservations" chose not to vote against the U.N. Security Council resolution authorizing military action in Libya.
Medvedev defended that decision on Monday, saying he did not consider the resolution wrong.
Putin, in some of his harshest criticism of the United States since President Barack Obama started a push for better ties, compared action on Libya to the Iraq invasion and said it showed Russia was right to spend billions on its military.
He told workers at a missile factory in Votkinsk in central Russia that the U.N. Security Council resolution was flawed and it "resembles medieval calls for crusades."
Moscow has called on the United States, Britain and France to halt air strikes that are killing civilians, as alleged by Tripoli but strongly denied by the Pentagon.
Gates, speaking in St. Petersburg at the start of his two-day visit to Russia, told Interfax the mission was to establish a no-fly zone and "prevent a humanitarian disaster, to prevent Gaddafi from slaughtering his own people."
"I think we've made a lot of progress just in a couple of days toward accomplishing those two objectives," he said in an interview with the news agency.
Putin made his comments on the same day that Gates, a former CIA director expected to retire from government later this year, spoke to naval officers in Russia's second city about improving ties between the former Cold War foes.
Gates pointed to Moscow's help in setting up the Northern Distribution Network, a key supply route for the war in Afghanistan, and urged cooperation on missile defense.
"If you'd told me when I joined the CIA in 1967 that I would end my career helping to forge a stronger defense relationship with the Russians, I'd have been more than a bit skeptical," Gates told Russian naval officers on Monday in St Petersburg.
A holdover from the Bush administration, Gates saw first hand the U.S.-Russia relationship deteriorate over Russia's 2008 war against pro-western Georgia, and then improve under Obama.
Obama's effort to "reset" ties was crowned with the New START nuclear arms pact which came into force last month. It limits each country to 1,550 deployed strategic warheads and 800 delivery systems by 2018.
Russia's chief negotiator on the nuclear arms treaty with the United States has outlined tough conditions for further reductions, stressing Moscow's demand for an equal say in creating a European missile shield.
Moscow worries the shield could weaken Russia's offensive arsenal and upset the balance of power.
"The United States would far prefer to have Russia as a partner in European missile defense," Gates told Interfax.
"I think that we can provide political assurances that would reassure Russia that no aspect of our missile defense is ever intended to be used against Russia," he told the news agency.
(Editing by Louise Ireland)