* Putin ignores rebels' calls for military help
* Russian leader signals he favours de-escalation
* Putin may have achieved main goals
* Russia wary of threat of more Western sanctions
MOSCOW, July 7 (Reuters) - Three weeks before Ukraine's army forced rebel fighters out of the strategic eastern city of Slaviansk, their commander made a desperate plea for military help from Russia.
"A week will pass, two, three, maybe a month, and the rebellion's best fighters will be bled dry and, sooner or later, crushed and destroyed," Igor Girkin, who is better known as Strelkov, said in a comments widely viewed online.
The appeal was met with silence by President Vladimir Putin, and on Saturday, as if on cue, Girkin's outnumbered and outgunned forces abandoned the city after weeks of shelling.
The weekend's events may be not just a turning point in Ukrainian President Petro Poroshenko's military campaign against the rebellion led by separatists who want eastern Ukraine incorporated into Russia.
They could also suggest Putin is not about to replay in eastern Ukraine the sequence of events that led to Russia's annexation of Crimea in March and that he is intent on de-escalating the crisis to avert the risk of new Western sanctions and reduce the threat of instability on Russia's border.
In the past few weeks, he has withdrawn most troops massed near the frontier, asked parliament to cancel a resolution approving the use of military force in Ukraine and engaged in diplomacy with the West. Moscow has also signalled a willingness to allow stronger controls at the border, through which Ukraine says the rebels have received military supplies.
Barring a dramatic turn back towards armed intervention by Russia, Putin's goal appears to be to find a way to reduce tension in Ukraine without losing face or popularity.
"As a result of four months of aggression in Ukraine, Putin found himself at a fateful fork in the road," former Kremlin adviser Andrei Illarionov wrote in a blog posted on the website of liberal Russian radio station Ekho Moskvy on Saturday.
Abandoning the rebels risks a loss of support and could fuel opposition to Putin in Russia, he said, but the other choice - sending in the armed forces - would lead to an inevitable confrontation with the West.
FEARS OF INVASION RECEDE
Putin's popularity has risen to new highs over his handling of the Ukraine crisis, in which the toppling of a president sympathetic to Moscow threatened in February to end Russia's ability to influence events in a country it long dominated.
The reclaiming of Crimea in March stirred patriotism and won Putin almost unanimous praise at home, though the rebellion that followed in eastern Ukraine raised fears in the West that Moscow was about to send in troops, despite his denials that Moscow was orchestrating the uprising and supporting it militarily.
Putin reiterated in a speech to Russian ambassadors gathered in Moscow last week that he reserved the right to protect Russian speakers abroad by "using the entire range of available means - from political and economic to operations under international humanitarian law and the right of self-defence."
But he has signalled repeatedly that he wants to reduce tensions - even though he may wish to keep them simmering just enough to unsettle Ukraine's pro-western leadership.
Loath as he is to say it, Russia is increasingly worried that sanctions could inflict serious damage on its $2 trillion economy, which is already heading towards recession, potentially denting Putin's popularity.
The reduction in tensions so far has helped strengthen the rouble and Russian shares, which rose last week to eight-month highs before slipping back.
This makes it no surprise that he had by late Monday made no public comment on the fall of Slaviansk, while Foreign Ministry remarks and state media coverage focused on humanitarian problems and the ferocity of the government forces' onslaught.
Russia also sent a positive sign on its commitment to talks at the weekend by attending the latest meeting on ending the violence under the auspices of the Organization for Security and Cooperation in Europe (OSCE).
Putin could have another reason for de-escalation; he may already have achieved all he can in Ukraine, at least for now.
He may be gambling that what is already on offer from Kiev could be enough to satisfy the nationalist sentiment he has unleashed in Russia but could yet struggle to contain.
Poroshenko has drawn up a peace plan that includes promises of decentralisation and more power for the regions, such as the rebellious provinces of Donetsk and Luhansk, enabling them to build political and economic ties with Moscow.
The plan also offers guarantees for the rights of Russian speakers, one of the main demands set out by Russia and the separatists throughout the conflict.
Russia had sought a "federal" Ukraine where power was devolved even further and still wants Russian peacekeepers allowed into east Ukraine, despite concerns abroad that it might try to use them to resupply the rebels.
But the moves already outlined by Poroshenko offer Moscow an opportunity to maintain some influence in Ukraine, a former Soviet republic and a territory that many Russians consider the cradle of Russian civilisation.
Putin has also won what appears to be the most important concession of all for him - a step back by the Kiev leadership from a commitment to seeking NATO membership.
Putin has made clear many times that Moscow will not allow Ukraine to join the alliance that was its Cold War enemy because doing so would represent too much of a security threat.
"What did our partners expect from us as the developments in Ukraine unfolded?" Putin asked the ambassadors last week.
Answering his own question, he said Russia could not abandon Crimea "to nationalist and radical militants", let its access to the Black Sea be limited - it has a naval base in Crimea - or allow NATO on to "the land of Russian military glory".
"This would mean giving up practically everything that Russia had fought for since the times of Peter the Great, or maybe even earlier - historians should know," he said. (Editing by Will Waterman)