MOSCOW (Reuters) - Presidents Dmitry Medvedev and Barack Obama meet in London on Wednesday to try to "reset" thorny Russia-U.S. ties and find ways for the two biggest nuclear powers to cooperate on key global issues. While their predecessors Vladimir Putin and George W. Bush relied on personal chemistry to survive policy rows, Medvedev and Obama have vowed to be pragmatic in handling contentious issues like arms control, missile defense, Iran and Afghanistan.
Both sides say the most likely concrete outcome of the London meeting will be an agreement to start talks on a new treaty limiting long-range nuclear missiles to replace a pact which expires this year.
Medvedev and Obama are both former lawyers in their forties. The Russian leader has welcomed Obama's intention to leave behind what Moscow saw as Washington's confrontational approach over the past few years and has praised a letter from Obama outlining international priorities.
"Frankly speaking, when I was reading it I was surprised by the fact that many views outlined there coincided with my ideas," Medvedev said in a weekend interview to BBC television.
"The question, certainly, is how we shall be able to present our views during our personal meeting," he added. "To what extent our teams are ready ... to break stereotypes."
An Obama aide was equally positive in recent comments.
"Our sense is that the atmospherics around our relationship with Russia have dramatically improved over the last several weeks," Denis McDonough, a deputy national security adviser to Obama, told reporters in Washington on Saturday.
"...the bottom line is, I think: we've seen some very positive things over the past several weeks and we look forward to seeing if we can't put those into action," he added.
But deep policy disagreements mean both sides are wary.
Despite warm personal relations between Bush and Putin, Russian-U.S. relations came to a standstill last year amid rows over U.S. plans to deploy elements of its anti-missile system in central Europe and Russia's war in ex-Soviet Georgia.
The United States is suspicious of Russia's warm ties with U.S. foe Iran, while Moscow deplores Washington's drive to grant NATO membership to ex-Soviet Ukraine and Georgia.
After taking office, Obama sent signals to Moscow that NATO expansion was off Washington's books at least for now.
Medvedev's foreign policy adviser Sergei Prikhodko said the London meeting was expected to give an impetus to cooperation rather than to solve all the problems.
"We understand that to an extent their first meeting will be a mutual try-out," he told reporters on Friday. "Being realists, we understand too well the contradictions dividing us and have no illusions that they can be left behind easily."
Arms reductions, an important but less contentious issue in bilateral ties, offers the best chance of early progress.
The 1991 Strategic Arms Reduction Treaty (START) expires in December. Differences on how to follow it up have stalled work on a replacement deal until now.
Prikhodko said Medvedev and Obama were likely to come out with a statement which would give guidelines to negotiators.
Russia links further arms reductions with the anti-missile issue. It wants Washington to give up its anti-missile plan and work with Moscow on a new joint project.
Afghanistan, where a U.S.-led force is fighting the Taliban, may be another area where "pressing a reset button" in bilateral ties -- to use a phrase first coined by U.S. Vice President Joe Biden in February -- could bring quick results.
Russia has allowed non-lethal supplies for NATO forces in Afghanistan through its territory by rail, a vital complement to the existing supply route through Pakistan. But, in a conflicting signal, it has encouraged its ex-Soviet ally Kyrgyzstan to shut a U.S. air base.
Some analysts in Moscow have noted that former president and now Prime Minister Putin -- hawkish on the U.S. and still highly influential on foreign policy -- will not be present at the London meeting.
Medvedev insisted in his weekend interview that he was in sole charge of policy as president but polls consistently show most Russians still think Putin is running the show.
(Additional reporting by Matt Spetalnick in Washington)