* Serbia seeks to maintain balance between EU and Russia
* Belgrade stands alone outside NATO in Western Balkans
* EU-Russia tensions over energy, security run through Serbia
By Luke Baker and Aleksandar Vasovic
LONDON/BELGRADE, Nov 28 (Reuters) - Since October, French President Emmanuel Macron has questioned the effectiveness of NATO, hit pause on EU enlargement and called for a new 'strategic relationship' with Russia.
Plenty of countries have reason to pay close attention to his "shake it up" style of diplomacy, but few places will feel his words more keenly than Serbia.
For Belgrade, any pullback by Europe or NATO could allow space for Russia to fill the void, given the close political, military and economic ties Moscow has with its Balkans cousin - a fellow Slavic and Orthodox Christian state.
That is likely to be of concern for NATO leaders, who gather in Britain next week to discuss the future of their military alliance, since the Balkans, much like the Baltics, can be seen as a bulkhead against Moscow's influence.
"NATO works to promote stability, security and cooperation in the Western Balkans," said a NATO official. "Any outside interference in domestic democratic processes is unacceptable. We urge Russia to do the same."
In a recent example of alleged interference, Serbian intelligence agencies uncovered evidence of Russian spies building contacts with former members of the Serbian military.
Russia's foreign ministry played down the report, calling it a "provocation", while Serbian President Aleksandar Vucic said it wouldn't harm relations between the two, adding he was sure President Vladimir Putin "was not informed about this".
OUT OF NATO
Alarm bells for the region rang in mid-October, when Macron refused to sign off on allowing Albania and North Macedonia, two of Serbia's neighbours, to begin talks on joining the EU.
Macron has grown increasingly wary of EU expansion, arguing that the 28-country group needs to take stock of its near doubling in size over the past 15 years, assess the impact of Britain's pending departure, and think hard about the criteria it applies to those seeking to join.
While Serbia has already begun membership talks, it now feels the chill of Macron's refusal to open the door to others on its patch.
At the same time, while nearly all surrounding countries have joined or are about to join NATO, Serbia remains out and is committed to neutrality, the memory of NATO's bombing of its territory during the 1999 Kosovo war still fresh.
It does belong to NATO's "partnership for peace" and takes part in NATO exercises, but its military has ties to Russia and Moscow provides technology and patronage, recently deploying its S-400 missile-defence system in Serbia for training.
Russia also regularly supplies fighter jets, surface-to-air missiles and other weaponry.
For the EU, much of the problem lies in what it sees as weak rule of law in Serbia, analysts said.
"What is worrying for the EU is not so much Russia but the circumstances that allow Russia to have influence - lack of the rule of law, lack of accountability, state capture, corruption," said Dimitar Bechev, a non-resident fellow at the Atlantic Council and a specialist on Russian influence in the region.
"They are local phenomena, but Russia knows how to operate in such an environment and is empowered by it."
In its latest assessment of Serbia's progress in meeting the criteria for joining the EU, Brussels flagged its concerns about corruption as well as Belgrade's failure to align with the EU on restrictive measures imposed on Russia.
While Moscow does not have the money to match either China or the European Union for spending and investment in the region, it still has considerable leverage.
Turkstream, a pipeline to supply Russian gas to Europe while bypassing Ukraine, is set to run via Bulgaria and Serbia before arriving in Hungary and supplying Germany, Austria and others.
That makes Serbia a critical link in the EU's energy pipeline, similar to the role Ukraine played as gas transshipper to the EU before falling foul of Moscow.
Milan Karagaca, a former military diplomat and a member of Belgrade's Centre for Foreign Policy think-tank, doesn't think Russia has grand plans to exploit Serbia strategically, but sees it "as a pawn in its great game with the West".
Serbia's task is to remain on good terms with Moscow, convince Brussels it is doing what's required to become an EU member state and avoid alienating NATO.
A government official, who declined to be named, said Serbia intended to maintain a balance between Russia and the West.
"No country or international body can claim they have us within their sphere of influence," he said.
Whatever the outcome, Serbia risks ending up being a small piece in a larger game of geopolitics that has sped up since Macron took NATO to task and questioned Europe's capabilities.
"If the West is disengaged and lets the region go then Russia has lots of opportunities to get mileage out of the situation," said Bechev.
On the other hand, if Serbia does join the EU, Bechev says it could become akin to Cyprus or Hungary, two member states with close ties to Moscow.
"Serbia will be weak or pro-Russian if they end up in the EU, which is no bad outcome for Russia either," he said. (Writing by Luke Baker; Additional reporting by Robin Emmott in Brussels; Editing by Mike Collett-White)