* Ukraine leader flies to Sochi, expected to meet Putin
* May discuss PM, Putin may echo aide's call for crackdown
* Kremlin adviser says US arming rebels, blackmailing Kiev
* Internet "leaks" of US, EU diplomats smack of dirty tricks
* Cold War echoes as Moscow warns could intervene in Ukraine
By Alastair Macdonald
KIEV, Feb 6 (Reuters) - Ukraine's embattled president flew to Russia on Thursday as a senior Kremlin aide urged him to stamp out a standoff on the streets, calling it an attempted coup financed and armed by the United States.
Caught in a rip-tide of competing enticements and threats from Russia and the West, President Viktor Yanukovich flew to Sochi where he was expected to meet Vladimir Putin before the Russian leader opens the Winter Olympics on Friday evening.
The bitter tug-of-war going on between east and west broke out into dirty tricks on the Internet, with what appeared to be online leaks of bugged recordings of top U.S. and EU diplomats discussing efforts to help Yanukovich's opponents into power.
And the Kremlin aide, a key Putin adviser on Ukraine, added to the Cold War ambience of Russia's first Olympics since 1980 by warning that Moscow could intervene to defend Ukraine's sovereignty under the terms of the 1994 pact with the United States under which Kiev gave up nuclear weapons inherited from the Soviet Union.
For the time being, however, that seemed a distant threat.
Yanukovich, who triggered mass protests in November when he yielded to Russian pressure and backed out of a free trade pact with the European Union, may tell Putin of his plans for a new government.
Moscow has frozen aid it granted after the EU debacle until it knows who Yanukovich names in place of the pro-Russian prime minister removed last week in a bid to appease opponents.
The leader of the biggest opposition party turned down an offer to be premier last week. Opposition figures speculate that Yanukovich may now name one of his own hardline allies.
Putin may voice some of the impatience with Yanukovich that was expressed by the Kremlin's point man on Ukraine; Sergei Glazyev, in a typically confrontational newspaper interview, urged the Ukrainian leader to crack down instead of negotiating with "putschists" whom he accused Washington of arming, funding and training to take over the ex-Soviet state.
In a stark reminder of his dilemma of competing choices, before heading for Sochi, Yanukovich met senior U.S. envoy Victoria Nuland. He assured her, according a statement from his office, that he wanted talks not violence: "Only by dialogue and compromise can we get out of this crisis," he said.
The United States and European Union have urged Yanukovich to form a consensus government involving the opposition and to embark on constitutional and economic reforms which would bring Western financial and other aid to the nation of 46 million.
Alarmed by violence in which at least six people were killed and dozens of others have been wounded or gone missing, Washington and Brussels have also brandished threats of sanctions, particularly travel bans and asset freezes targeted at officials and others involved in repressing dissent.
Kremlin aide Glazyev accused Nuland of "blackmail" by privately warning wealthy, mostly Russian-speaking oligarchs who back Yanukovich that they risked their foreign assets being seized if they did not hand power to the opposition.
U.S. officials did not respond directly to Glazyev's remarks, which included an allegation U.S. agents were giving "$20 million a week" for to "the opposition and rebels" and that "within the grounds of the American embassy, there is training for fighters" being armed by Washington.
U.S. officials would also not discuss a YouTube recording that purported to be a phone call between Nuland and the U.S. ambassador. Posted anonymously, with subtitles in Russian, it was clearly intended to portray opposition leaders as "puppets" of the U.S. diplomats, who were discussing how the opposition might take up an offer from Yanukovich to form a government.
Smacking of dirty tricks in great power arm-wrestling over Ukraine that has echoes of the Cold War, the recording included what sounded like Nuland making a crude dismissive remark about the EU and the ambassador warning that the Russians would work "behind the scenes" to "torpedo" an opposition-led government.
From the same YouTube account, which has previously carried video showing protesters in a poor light, a recording was posted on the same day, Tuesday, purporting to be of a senior EU official talking to the bloc's envoy in Kiev. They discuss annoyance that U.S. officials were briefing the media that by holding back on sanctions the EU was too "soft" on Yanukovich.
A spokeswoman for EU foreign policy chief Catherine Ashton, who met Yanukovich and opposition leaders in Kiev on Wednesday, said the EU would not comment on "leaked alleged" conversation.
The simultaneous release of the recordings, whatever their source and authenticity, appeared designed to both discredit the Western powers' involvement in Ukraine and, possibly, to drive a wedge between Brussels and Washington.
The European Parliament voted on Thursday for sanctions - including cancelled EU visas and frozen assets - on those responsible for violence against demonstrators. EU governments are loath to take such action against Yanukovich for now.
A poisonous confrontation between the president, whose power base lies in the Russian-speaking industrial east, and opponents, many from the Ukrainian-speaking west who view him as a corrupt pawn of the Kremlin, has been marked by mutual allegations of violence and intimidation that have prompted fears of a civil war that could spill across the continent.
An activist, whose account of his "crucifixion" after being abducted fuelled opposition anger last week, said from the Lithuanian clinic where he is being treated that his torturers made him say on camera that he was a U.S. agent.
Several thousand demonstrators marched without incident on Thursday to the parliament building where the deeply divided legislature agreed to try and draft a bill in committee in the coming days to amend the constitution.
The opposition wants to restore a version of the basic law that gave parliament more power over the government. However, Yanukovich supporters have been the majority. The president's allies, still leading opinion polls with about 20 percent in a fragmented field, say stalemate could mean new elections.
Putin adviser Glazyev was asked by Kommersant-Ukraine newspaper whether Russia might "actively intervene".
Recalling the Budapest Memorandum of 1994, which removed Soviet nuclear weapons from Ukraine, he said: "Under the document, Russia and the USA are guarantors of the sovereignty and territorial integrity of Ukraine and ... are obliged to intervene when conflict situations of this nature arise."
Asked by the paper if Yanukovich should now use force to clear the protesters, Glazyev said: "As for starting to use force, in a situation where the authorities face an attempted coup d'etat, they simply have no other course of action."
Russia, he said, was concerned that the country should not split apart. But he suggested that a form of federalism be introduced to give regions substantial powers - to the extent eastern regions might be linked to a customs union with Russia while western Ukraine might have a trade pact with Europe. (Additional reporting by Natalia Zinets and Jack Stubbs in Kiev; Reporting by Alastair Macdonald; Editing by Andrew Heavens)