A slow-moving effort to hold an inquest into the poisoning death of a Russian whistle-blower, Alexander V. Litvinenko, moved ahead on Thursday in London, with the British authorities insisting in a preliminary hearing that possible contacts between him and the British secret intelligence service MI6 should not be disclosed.

While there was no immediate ruling on the secrecy claim, associates of Mr. Litvinenko expressed confidence that the restrictions would be lifted.

Mr. Litvinenko, a former K.G.B. officer and critic of the Russian authorities who had won asylum and citizenship in Britain, died in November 2006 after ingesting a rare radioactive isotope, polonium 210, from a teapot at a meeting with Russian contacts at the Millennium Hotel in Grosvenor Square in London.

Mr. Litvinenko’s death, coinciding with other strains between London and Moscow, chilled relations between Britain and Russia, leading to tit-for-tat expulsions of diplomats reminiscent of the cold war. Russia’s refusal to hand over the man accused of killing Mr. Litvinenko has since stymied efforts to restore normal ties.