(Adds detail on diplomacy, referendum, situation in Crimea)
* Amid military standoff, Crimea prepares for vote
* Ukraine beefs up forces, seeks Western aid against Russia
* War of words continues over Crimea secession referendum
* Ukrainian PM chides West over nuclear disarmament treaty
By Andrew Osborn and Alastair Macdonald
SEVASTOPOL/KIEV, March 11 (Reuters) - Ukraine's government appealed for Western help on Tuesday to stop Moscow annexing Crimea but the Black Sea peninsula, overrun by Russian troops, seemed fixed on a course that could formalise rule from Moscow within days.
With their own troops in Crimea effectively prisoners in their bases, the new authorities in Kiev painted a sorry picture of the military bequeathed them by the pro-Moscow president overthrown two weeks ago. They announced the raising of a new National Guard to be drawn from volunteers among veterans.
The prime minister, heading for talks at the White House and United Nations, told parliament in Kiev he wanted the United States and Britain, as guarantors of a 1994 treaty that saw Ukraine give up its Soviet nuclear weapons, to intervene both diplomatically and militarily to fend off Russian "aggression".
But despite NATO reconnaissance aircraft patrolling the Polish and Romanian borders and U.S. naval forces preparing for exercises in the Black Sea, Western powers have made clear that, as when ex-Soviet Georgia lost territory in fighting in 2008, they have no appetite for risking turning the worst East-West crisis since the Cold War into a military conflict with Moscow.
Diplomacy seemed restricted to a war of words. The U.S. and Russian foreign ministers did speak by telephone. But the U.S. State Department said Moscow's position offered no room for negotiation and the Russian Foreign Ministry issued a statement condemning U.S. financial aid to the "illegitimate regime" in Kiev, which it calls ultra-nationalists with "Nazi" links.
That language echoed ousted Ukrainian president Viktor Yanukovich, who gave a news conference in Russia insisting that he was still the legitimate head of state. Toppled by protests sparked by his rejection of closer ties with the European Union in favour of a deal from Russian President Vladimir Putin, Yanukovich blamed his enemies for provoking Crimean secession.
Parliament in Kiev, whose position is backed by Western governments, dismisses plans for a referendum on Sunday to unite the region with Russia as illegitimate and resolved on Tuesday to dissolve Crimea's regional assembly if by Wednesday it had not scrapped the plebiscite. There seems no chance that it will.
Moscow, which to widespread scorn denies its troops have any role in the takeover of the once Russian-ruled region, says people in Crimea, a small majority of whom are ethnic Russians, should have the right to secede. It has made much of anti-Russian sentiment among some Ukrainian nationalists - though many native Russian speakers in Ukraine are wary of Putin.
U.S. lawmakers are preparing sanctions against Russia and European Union leaders could impose penalties, such as bans on visas for key officials, as early as Monday.
By then, however, Crimea could already have voted - in a referendum not recognised by Kiev or the West - to seek union with Russia. The ballot paper offers no option to retain the status quo of autonomy within Ukraine.
Voters among the two million population must choose either direct union with Moscow or restoring an old constitution that made Crimea sovereign with ties to Ukraine. On Tuesday, the regional assembly passed a resolution that a sovereign Crimea would sever links to Kiev and join Russia anyway.
The Russian parliament has already approved the accession in principle of Crimea, which was handed to Ukraine by Soviet rulers 60 years ago. Still, it is not clear whether or how soon Putin would formalise such a union as he engages in a complex confrontation with the West for geostrategic advantage.
In disputes with Georgia, Russia has granted recognition to small breakaway states on its borders, a process critics view as annexation in all but name. It fiercely criticised Western recognition of the independence of Kosovo from its ally Serbia - a process which Crimea's parliament nonetheless cited as a legal precedent for its own forthcoming declaration of independence.
There seems little chance that Crimea's new leaders, who emerged after Yanukovich's overthrow as Russian-backed forces took control of the peninsula, will fail to get the result they want. A boycott by ethnic Tatars, 12 percent of the regional population and deeply wary after centuries of persecution by Moscow, will have little effect as there is no minimum turnout.
In Sevastopol, the Crimean home port of Russia's Black Sea Fleet, Valery Medvedev, the chairman of the city's electoral commission, made no pretence at concealing his own preference:
"We're living through historic times. Sevastopol would love to fulfil its dream of joining Russia. I want to be part of Russia and I'm not embarrassed to say that," he told reporters.
There is little sign of campaigning by those opposed to the government line. Billboards in Sevastopol urge people to vote and offer a choice of two images of Crimea - one in the colours of the Russian flag, the other emblazoned with a swastika.
It is unclear whether thousands of Ukrainian servicemen, many of whom are native Crimeans but are effectively trapped on their bases and ships by Russian troops and local militia allies, will take part in the referendum.
One sailor, who declined to be named, said he would only vote if he got the order from his commander to do so, a position echoed by many other servicemen spoken to by Reuters. They all said they would vote for Crimea to remain part of Ukraine.
Elena Prokhina, an ethnic Russian planning to vote for union with Moscow, said she feared the referendum could lead to conflict with others in Ukraine, notably nationalists in the Ukrainian-speaking west of the country of 46 million.
"Knowing what I know about the fanaticism of the western Ukrainians, we will have to defend our rights after the referendum," she said. "They won't just let us leave."
Around Sevastopol, Ukrainian military facilities remained under virtual siege on Tuesday. At an air defence base outside Sevastopol, dozens of men who looked like Russian soldiers were camping outside the gate, while an armed Ukrainian serviceman could be seen pacing the base's roof keeping a wary eye on them.
In the port, two Ukrainian warships remained on alert but unable to set sail because of Russian vessels and a cable strung across the harbour by Russian forces. Relatives of the sailors come to the dockside every day to converse and provide food.
A Ukrainian officer said there was a fragile understanding between the two fleets not to escalate the situation, but he said nerves were frayed: "The Russians have not troubled us until now," he said. "But all it takes is one order and they will open fire. We won't be able to hold out long".
CALL FOR HELP
In parliament, the acting defence minister said that of some 41,000 infantry mobilised last week, Ukraine could field only about 6,000 combat-ready troops, compared to over 200,000 Russians deployed on the country's eastern borders. The prime minister said the air force was outnumbered 100 to one.
Acting president Oleksander Turchinov warned against provoking Russia, saying that would play into Moscow's hands, as he announced plans to mobilise a National Guard, though he gave little detail of its size or expected functions.
Prime Minister Arseny Yatseniuk, who will visit the White House and United Nations Security Council this week, said the 1994 treaty under which Ukraine agreed to give up its Soviet nuclear weapons obliged Russia to remove troops from Crimea and also meant Western powers should defend Ukraine's sovereignty.
"What does the current military aggression of the Russian Federation on Ukrainian territory mean?" he said.
"It means that a country which voluntarily gave up nuclear weapons, rejected nuclear status and received guarantees from the world's leading countries is left defenceless and alone in the face of a nuclear state that is armed to the teeth.
"I say this to our Western partners: if you do not provide guarantees, which were signed in the Budapest Memorandum, then explain how you will persuade Iran or North Korea to give up their status as nuclear states."
Parliament passed a resolution he had proposed calling on the United States and Britain, co-signatories with Russia of that treaty to "fulfil their obligations ... and take all possible diplomatic, political, economic and military measures urgently to end the aggression and preserve the independence, sovereignty and existing borders of Ukraine".
But Western powers have been careful to note that Ukraine, not being a member of NATO, has no automatic claim on their help and Ukrainian officials gave no details on what they hoped for. The wording of the 1994 treaty indicates that help is only required if Ukraine is threatened by a nuclear attack. (Additional reporting by Natalia Zinets, Pavel Polityuk, Richard Balmforth and Ron Popeski in Kiev; Writing by Alastair Macdonald; Editing by Peter Graff)