WASHINGTON (Reuters) - Three months into his military intervention in Syria, Russian President Vladimir Putin has achieved his central goal of stabilizing the Assad government and, with the costs relatively low, could sustain military operations at this level for years, U.S. officials and military analysts say.

A frame grab taken from footage released by Russia's Defence Ministry December 25, 2015, shows air strikes carried out by Russia's air force hitting militants' vehicles, which, according to the ministry, carried oil, at an unknown location in Syria. REUTERS/Russian Defence Ministry/Handout via Reuters

That assessment comes despite public assertions by President Barack Obama and top aides that Putin has embarked on an ill-conceived mission in support of Syrian President Bashar al-Assad that it will struggle to afford and that will likely fail.

“I think it’s indisputable that the Assad regime, with Russian military support, is probably in a safer position than it was,” said a senior administration official, who requested anonymity. Five other U.S. officials interviewed by Reuters concurred with the view that the Russian mission has been mostly successful so far and is facing relatively low costs.

The U.S. officials stressed that Putin could face serious problems the longer his involvement in the more than four-year-old civil war drags on.

Yet since its campaign began on Sept. 30, Russia has suffered minimal casualties and, despite domestic fiscal woes, is handily covering the operation’s cost, which analysts estimate at $1-2 billion a year. The war is being funded from Russia’s regular annual defense budget of about $54 billion, a U.S. intelligence official said.

The expense, analysts and officials said, is being kept in check by plummeting oil prices that, while hurting Russia’s overall economy, has helped its defense budget stretch further by reducing the costs of fueling aircraft and ships. It has also been able to tap a stockpile of conventional bombs dating to the Soviet era.

Putin has said his intervention is aimed at stabilizing the Assad government and helping it fight the Islamic State group, though Western officials and Syrian opposition groups say its air strikes mostly have targeted moderate rebels.

Russia’s Syrian and Iranian partners have made few major territorial gains.

Yet Putin’s intervention has halted the opposition’s momentum, allowing pro-Assad forces to take the offensive. Prior to Russia’s military action, U.S. and Western officials said, Assad’s government looked increasingly threatened.

Rather than pushing back the opposition, Russia may be settling for defending Assad’s grip on key population centers that include the heartland of his minority Alawite sect, said the U.S. intelligence official.

Russia is taking advantage of the operation to test new weapons in battlefield conditions and integrate them into its tactics, the intelligence official said. It is refining its use of unarmed surveillance drones, the official added.

“The Russians didn’t go blindly into this,” said the U.S. intelligence official, adding that they “are getting some benefit out of the cost.”

QUAGMIRE?

Russia’s intervention also appears to have strengthened its hand at the negotiating table. In recent weeks, Washington has engaged more closely with Russia in seeking a settlement to the war and backed off a demand for the immediate departure of Assad as part of any political transition.

Obama has suggested as recently as this month that Moscow is being sucked into a foreign venture that will drain its resources and bog down its military.

“An attempt by Russia and Iran to prop up Assad and try to pacify the population is just going to get them stuck in a quagmire and it won’t work,” Obama said on Oct. 2.

On Dec. 1, he raised the prospect of Russia becoming “bogged down in an inconclusive and paralyzing civil conflict.”

The senior administration official denied any contradiction between Obama’s statements and private assessments that Russia’s campaign has been relatively effective so far.

“I think the president’s point has been...it’s not going to succeed in the long run,” the official said. The Russians “have become bound up in a civil war in a way that’s going to be extremely difficult to extricate themselves from.”

U.S. officials have not publicly defined what a quagmire would look like for Russia. But Obama has raised the Soviet Union’s disastrous decade-long Afghanistan occupation from 1979.

U.S. officials said Russia’s military footprint is relatively light. It comprises a long-time naval facility in Tartus, a major air base near the port city of Latakia, a second under expansion near Homs and several lesser posts.

There are an estimated 5,000 Russian personnel in Syria, including pilots, ground crews, intelligence personnel, security units protecting the Russian bases and advisers to the Syrian government forces.

Russia has lost an airliner to an Islamic State-claimed attack over Egypt that killed 224 people, and an Su-24 supersonic bomber shot down by Turkey. It is also allied with an exhausted Syrian army that is suffering manpower shortages and facing U.S.-backed rebels using anti-tank missiles.

“It’s been a grind,” said the intelligence official, adding that in terms of ground gains, “I think the Russians are not where they expected to be.”

Russian casualties in Syria have been relatively minimal, officially put at three dead. U.S. officials estimate that Russia may have suffered as many as 30 casualties overall.

Vasily Kashin, a Moscow-based analyst, said the war is not financially stressing Russia.

“All the available data shows us that the current level of military effort is completely insignificant for the Russian economy and Russian budget,” said Kashin, of the Center for Analyses of Strategies and Technologies.

“It can be carried on at the same level year after year after year,” he said.