A meeting between the Russian President Vladimir Putin and US President George W. Bush was reported to have made progress but no deal.
Russian Trade Minister German Gref said agriculture was the main obstacle to Russian gaining entry to the WTO.
US negotiators wanted to ensure Russian restrictions on food imports were consistent with WTO rules.
Progress was reported on other issues, including access to Russia's banking and insurance markets and enforcement of Russia's anti-piracy laws.
American officials said they hoped a deal could be finalised in the coming months.