MOSCOW Hope that a shift in U.S. missile defense strategy will improve relations with Russia risks being undermined by a fresh flare-up over human rights when President Barack Obama's top security aide visits Moscow on Monday.
A change in U.S. plans for an anti-missile shield in Europe has cracked the door open for compromise on an issue that has badly strained relations between the nuclear-armed former Cold War foes.
But a big obstacle looms before White House national security adviser Tom Donilon even arrives.
President Barack Obama will give Congress on Friday a list of Russians to be barred from the United States for suspected involvement in human rights abuses including the 2009 death of whistleblower Sergei Magnitsky in a Moscow jail.
Russia has warned it would swiftly retaliate with its own list of unwelcome Americans in a tit-for-tat response that could cloud any prospect for progress on missile defense.
"If the list is published, we will react, and our American partners know that," Russia's Foreign Minister Sergei Lavrov said on Friday.
"The choice of timing was not entirely favorable, considering that ... Mr. Donilon is coming to give a message from President Obama with a broad vision of the prospects for Russian-American cooperation."
President Vladimir Putin's spokesman, Dmitry Peskov, said issuing the names would have a "very negative effect" but he also sought to limit the damage by adding there would still be plenty of room for improvement in the multifaceted relationship.
Threatened with attack by North Korea, the United States said last month it would deploy more missile interceptors in Alaska while scrapping plans for an upgraded interceptor meant to be deployed in central Europe by about 2020.
That wipes out what the Kremlin has called its main concern about the European shield: that its interceptors could shoot down long-range Russian missiles, weakening Moscow's nuclear deterrent and upsetting the balance of power with the West.
Russia has responded cautiously, however, and any shift in Moscow's position would come from Putin.
"That's the big question mark on everybody's minds - how will he react," said Samuel Charap, a senior fellow at the International Institute for Strategic Studies in Washington.
"The visit is just the beginning of the beginning. If the U.S. were convinced that Putin has absolutely no interest, they would not have sent the most senior national security official in the White House to talk to him," he said.
Progress over missile defense could help clear a path for further cuts in nuclear arsenals following the 2010 New START treaty, the showpiece of Obama's first-term push to "reset" relations with Russia.
Ties soured again after Putin started his march back to the presidency in 2011, when he accused the United States of encouraging opposition protests. The countries are also at odds over the war in Syria and Putin's treatment of his opponents.
Relations worsened further after Congress passed the Magnitsky Act in December to respond to the death in custody of a Russian lawyer who had accused police investigators of stealing $230 million from the state through fraudulent tax returns, a death his supporters say was suspicious.
Russia responded to the Magnitsky Act with similar measures and banned adoption of Russian children by Americans, adding to a poisonous atmosphere that progress on missile defense could help ease.
"I certainly hope that the Russian side will look carefully at what we have done and draw some conclusions that could move us forward," John Beyrle, U.S. ambassador to Russia from 2008 until January 2012, said during a visit to Moscow this month.
Some Western diplomats suspect the Kremlin has been using its concern over the European missile shield as a bargaining chip and will continue to do so, but Putin could cast progress on the issue as a victory.
"A compromise on the shield could be useful for Putin if he can sell it by telling Russians the danger of the United States deploying missiles close to our borders is now gone because he put pressure on Obama," said Moscow-based analyst Georgy Mirsky.
At the heart of the confrontation is Russia's demand for a binding guarantee the missile shield would never threaten its security. The United States and its NATO allies have rejected that demand.
Any progress is likely to be slow, and rancor over the Magnitsky Act is a potential roadblock.
U.S. lawmakers and rights groups have urged a number of people be on the "Magnitsky list", including Chechnya's Kremlin-backed leader Ramzan Kadyrov and Alexander Bastrykin, head of the federal Investigative Committee, which answers to Putin.
A congressional source told Reuters on Friday there would be 18 people on the list, 16 of whom are suspected of being involved in the Magnitsky case.
"It is matter of honor for the Russian authorities not to back down on the Magnitsky issue. The United States also cannot turn a blind eye to it, so this is a deadlock," said Mirsky.
A gauge of whether Putin wants to improve ties will be whether he limits Moscow's response to naming Americans barred from Russia in retaliation, or if he goes further.
"If it stops there, then that is a tit-for-tat and it's OK," Steven Pifer, an expert on Russia at the Brookings Institution in Washington. "But if Moscow wants to use it for something else, then it's going to make it harder to focus on work in areas where there are some real equities in common."
(Editing by Steve Gutterman and Robin Pomeroy)