In the 12 days since he arrived in the Kremlin, the retired general has already played a leading part in a sweeping shake-up in the government, with the firing of the head of the Federal Security Service, the defence minister, the head of the presidential guard, a top aide and seven army generals. Should he get his way, this will only be for openers.
If Mr Yeltsin - said to be resting yesterday after weeks of heavy campaigning - is re-elected in Wednesday's run-off, his protege will seek a tranche of new powers, altering the relationship between different organs of government. Were Mr Lebed's dreams to be realised, there is every reason to believe that Russia, with its weak parliament, will be even less democratic than it is now. The former paratrooper general would also find himself in fierce conflict with the generals, security chiefs and the array of corrupt government officials whom he plans to challenge.
When Mr Lebed won nearly 11m votes in the election's first round a fortnight ago (with the Kremlin's help), Mr Yeltsin appointed him as the secretary of his Security Council and national security adviser in a pre-planned manoeuvre aimed at winning over his supporters in the run-off. Overnight the general became one of the most powerful men in the country - although more because of his proximity to the president than through the powers inherent in his new posts.
The council, set up in 1992, is an influential advisory body to the president. Like the old Communist Politburo, its members comprise the government's heavyweights - notably, the top brass in defence and security, but also from the other ministries. However, it has no law-making powers; the constitution places most of the power in the hands of the president.
But Mr Lebed has big changes in mind for the future. He has made clear that he intends to ask Mr Yeltsin to boost the power of the council, as part of a drive to "radically increase the efficiency of law and order bodies". This is the only way to prevent Russia from being engulfed by crime, and to guarantee stability and progress, he argues.Last week, he submitted a plan to Mr Yeltsin to create a system to "co-ordinate all the power ministries" - apparently intended to give the council a supervisory role over the formidable Federal Security Service, the military and other security organisations. Although he did not publicly spell out his demands in detail, suspicions abound that he envisages the council as a near-authoritarian body, answerable only to the president.
A clue to his strategy camefrom the Russian news agency Interfax, which published details of a plan, allegedly endorsed by Mr Lebed, called "A New Approach to Problems of National Security". It talked of the state playing a larger role in the economy, of modifying Russia's "unjustifiably accelerated privatisation progress", and of taking strict control over the export of raw materials. The general also wanted tighter passport and visa regulations, and to reorientate spying activities toward Russia's economic interests. At first, Mr Lebed - who is usually more moderate - sought to distance himself from it, saying that work on it began before his appointment, and that it was incomplete. But, according to Interfax, he later confirmed that the document reflected his views.
Quite apart from its anti-Western and interventionist undertones, the document is a revealing indication of the powers which Mr Lebed appears to be hoping he, and the Security Council, will wield: his definition of national security clearly includes economic strategy and some aspects of foreign policy.
Later the general widened his brief still further at a meeting in Moscow of nationalist groups, dominated by Cossacks. Russian culture was "one of the cornerstones of our national security", he said, during a wild diatribe about the Western "sexual trash or violence or soap operas" that had flooded the country. Will his bulging portfolio also include protecting the airwaves from the highly popular Santa Barbara series and cleansing the news stands of pornography?
Or defending the faith? In the same speech, Mr Lebed revealed that he regarded Western religious sects, including the Mormons, as "mould and filth" which had been "artificially brought into our country with the purpose of perverting, corrupting, and ultimately breaking up our state". His remarks prompted a flurry of outrage, both among Russian liberals and abroad. Such was the frisson of alarm that the White House - staunch defenders of Mr Yeltsin - admitted that its officials were concerned.
Much of Mr Lebed's remarks can be probably be put down to election rhetoric. But he appears to be serious about his grandiose plans for the Security Council, and his credibility would suffer heavily if he failed to try to implement them. Whether he ever realises them is a different matter, however. Until Wednesday's election is over, the gruff general will remain the favoured son of Mr Yeltsin, who badly needs his votes. Afterwards, the president could choose to dump him. In the meantime, Western diplomats and Russian democrats are eying Mr Lebed warily, wondering how much power he plans to steal from his aging mentor, and what impact he will have on Russia's young democracy.
"Like a former Roman centurion, whom fortune and political upheaval had suddenly turned into the junior co-ruler of an aging emperor, Lebed is apparently hoping to pull the real strings of power in Russia, while Yeltsin officially occupies the throne, mostly indulging in tennis and vodka," Pavel Felgenhauer, a commentator on defence, wrote in the Moscow Times recently. A foreign diplomat put it more bluntly: "General Lebed is out of control."