Washington and Moscow will place the "highest priority" on reaching a deal on the Strategic Arms Reduction Treaty (START), US Secretary of State Hillary Clinton said Friday after a friendly meeting with Russia's foreign minister.

Talks on START made little progress during the presidency of George W. Bush, raising worries about the demise of the 1991 treaty, which limits the strategic atomic arsenals of both sides to 1,600 missiles and 6,000 warheads.

Obama's arrival has given fresh momentum towards an agreement but the two sides have much work and little time.

START expires on December 5 and the Obama administration is still assembling its Russia team while juggling other pressing issues such as Iran, the wars in Iraq and Afghanistan and the economic crisis.

The treaty, a lengthy document that details complex verification procedures, contains a provision that would allow it simply to be extended for five years by mutual consent.

Russia has resisted that option, though, insisting in recent years it wants to negotiate a new, updated and legally-binding treaty with a broader scope.

"The talks will be very, very difficult," said Sergei Koshelev, the deputy head of the Russian foreign ministry's security and disarmament department.

But Koshelev, who was speaking at a round-table discussion in Moscow last week with both US and Russian arms control experts, indicated that reaching agreement would be easier if relations continued to warm.

"To have a new document on December 5 ... above all it is necessary to have a clear change in the climate of Russian-US relations," Koshelev said.

Just half a year ago, those relations were mired in their worst crisis since the Cold War after Russia fought a brief war with US-allied Georgia.

Bush had already enraged Moscow with his plan to deploy a US missile shield in eastern Europe, which Russia sees as a threat to its security despite US assurances that it is directed against "rogue states" like Iran.

The missile shield spat was among the factors stalling progress in the START negotiations.

Russia says the talks must be broadened to include missile defence. But that was rejected by Bush administration, which in 2002 unilaterally pulled out the 1972 Anti-Ballistic Missile (ABM) treaty in order to proceed with its shield.

"The Russian side will insist that these questions of the interdependence of missile defence... and the questions of strategic arms reduction must be addressed in the new document," Koshelev said.

Both sides should make concessions on missile defence to move forward, said Edward Ifft, a former US diplomat and negotiator in the original START talks who is now a professor at Georgetown University in Washington.

"The US needs to take more seriously Russian concerns regarding future ABM systems, especially those close to Russian territory," Ifft said at the discussion.

"For its part ... Russia needs to recognise more fully US concerns regarding terrorism and rogue states, and this includes understanding US views on missile defences," he added.

Other wide gaps between the US and Russian positions are also likely to keep negotiators busy as they thrash out the terms of a new accord this year.

For instance Russia insists that a new treaty must limit not just the number of warheads but also the means of delivering them -- missiles, bombers and submarines.

The US meanwhile would prefer to keep the focus on warheads, in particular on "operationally deployed" warheads which are actually kept in missiles and bombers.

But Russia worries this would give the US too much "upload potential" -- in other words, that Washington could keep numerous warheads in storage and quickly alter the balance of power by "uploading" them onto missiles.

Even with those differences things can only improve from the Bush years, argued Roland Timerbaev, a retired Russian diplomat and veteran of US-Soviet arms control talks.

"The last few years were the worst in terms of arms control for the entire postwar period," Timerbaev said. "It cannot get worse. It can only get better."