Neave Barker, Al Jazeera's correspondent in Moscow, said both sides will sign a communique of understanding that will lead the way to a new arms treaty.
"The move is symbolic. Both Russia and the US possess about 95 per cent of all the world's weapons and they want to send a clear message to the rest of the world's nations," he said.
The broad aim is to reduce the number of deployed warheads below the 1,700-2,200 allowed under START-I, which expires in December.
But officials have said that the two sides are still some distance from a new treaty, with the new declaration expected to only set guidelines for negotiators.
"There certainly won't be an agreement on the end deal ... but I think you will see an announcement that indicates some progress toward reaching that objective," Gary Samore, a White House arms control specialist, said.
Obama, who is making his first official visit to Moscow, has said he intends to restore friendly ties between Russia and the US.
"I seek to reset relations with Russia because I believe that Americans and Russians have many common interests," he told Novaya Gazeta, the Russian opposition newspaper, on the eve of his visit.
He said there were "interests that our governments recently have not pursued as actively as we could have".
While Obama hopes to keep building pragmatic ties with Medvedev, his introduction to Vladimir Putin, Medvedev's predecessor and current Russian prime minister, is likely to be more strained.
Obama set the stage with a pre-trip assessment that Putin still had "one foot" planted in the Cold War.
Putin, who still has a significant role in Russian politics, rejected the criticism and insisted it was US policy that needed to be updated.
Al Jazeera's Rob Reynolds, reporting from Washington, said one of Obama's tasks will be to "figure out exactly who's in charge in the Kremlin".
"He says he has a very good relationship with Medvedev. But many people believe Putin is still the most powerful person in the Kremlin hierarchy, and that Obama needs to figure out exactly how to deal with Putin in addition to Medvedev," he said.
Obama is also expected to win the Kremlin's consent to ship weapons to Nato forces in Afghanistan across Russian territory.
The transit deal will open up a crucial corridor for the US as it steps up its fight against the Taliban in line with Obama's new Afghanistan strategy.
Deep divisions persist over US missile defence, Nato expansion and the 2008 Russia-Georgia war.
Obama acknowledged in the Novaya Gazeta interview that there were "Russian sensitivities" over the proposed US anti-missile shield.
But he made clear he would not accept any effort by Moscow to link arms-control talks to missile defence.
Moscow, which sees proposed missile-defence sites in Poland and the Czech Republic as a threat to its security, has insisted in recent weeks that the two issues are inseparable.