General Barsukov, 47, has until now been in charge of the personal safety of senior Kremlin officials other than the President. He is believed to be a protege of Mr Yeltsin's influential bodyguard, General Alexander Korzhakov. A recent photograph of Mr Yeltsin, taken before he went into hospital, showed Mr Korzhakov and Mr Barsukov at his side, two very burly figures.
The top job at the FSB fell vacant after Mr Yeltsin sacked Sergei Stepashin, along with two other ministers, for mishandling the Chechen hostage crisis in the southern town of Budennovsk in June. Mr Stepashin had been trying to reform the security service.
While a Yeltsin spokesman hinted that General Barsukov might be planning staff changes in the organisation, liberals were not convinced this would aid reform. The head of the Duma's Defence Committee, Sergei Yushenkov, an opponent of the war in Chechnya, said he was not pleased with the appointment.
Alexander Konovalov, a military expert, suggested it would be a good thing if FSB professionals took charge of operations, while their new boss remained a figurehead. But he said this was unlikely. "I think it is a negative appointment when a bodyguard becomes head of the intelligence service."
News of the appointment was leaked last week, but General Barsukov then said he knew nothing about it. Confirmation came only yesterday, when Mr Yeltsin, said by his aides to be "feeling well" after treatment for a mild heart attack, checked out of the Moscow Central Clinic. He has now gone to convalesce for an unspecified period in a sanatorium at Barvikha in the countryside west of the capital.
Aides have said that stress over Chechnya had contributed to the President's heart problems. He has been closely following the progress of peace talks in Grozny but yesterday's session again failed to produce a breakthrough to cheer him.
After days of expressing optimism, which hardly seemed well founded, the negotiators admitted yesterday that the issue of Chechnya's future political status remained a stumbling block.
A Russian envoy, Arkady Volsky, said that the Chechen leader, General Dzhokhar Dudayev, had not improved the atmosphere by making a defiant anti-Russian statement on Saturday. Nevertheless, the search for peace would go on.