President Boris Yeltsin fired Federal Security Service head Nikolai Kovalyov over the weekend, replacing him with a little-known but loyal functionary from the Kremlin administration.


No explanation was given for the dismissal of Kovalyov, who was generously praised Monday by Prime Minister Sergei Kiriyenko for his professionalism. But analysts say the move may be an attempt by the Kremlin to bring the Federal Security Service, which is the chief successor to the KGB, under tighter control.


It remained unclear whether Yeltsin intended to sack other key figures in the government. Analysts have said deputy prime ministers Oleg Sysuyev and Viktor Khristenko may be next in the firing line. However, Kiriyenko said Monday that Kovalyov's dismissal was the limit of the Cabinet reshuffle.


The presidential press service announced late Saturday that Kovalyov had been sacked. Former KGB spy and deputy head of the presidential administration Vladimir Putin, 45, was named as his successor.


Yeltsin, who is vacationing in Karelia, north of St. Petersburg, told reporters Saturday that he was about to dismiss a member of the Cabinet, but hinted only darkly at his reasons. "You don't know all the details," he said after a meeting with Kiriyenko, who had flown to Karelia for talks with the president. "That is why it seems incomprehensible to you. But I've had enough of it all."


At a meeting with the Federal Security Service, or FSB, top brass Monday morning, Kiriyenko emphasized that Kovalyov's dismissal was not a reflection of his poor performance.


"This is by no means a negative assessment either of his work or of the service as a whole," he said at the meeting on Lubyanskaya Ploshchad, the once universally feared headquarters of the KGB. "Kovalyov's experience, abilities and knowledge will doubtless be used for the good of the country. He has done a commendable job during his two years as FSB director."


Kovalyov, 49, an expert in counterespionage, was appointed to the post in 1996, shortly after Yeltsin was re-elected.


With no official reason given for Kovalyov's abrupt dismissal, rumors were rife as to the rationale behind it.


Some commentators said Kovalyov was sacrificed so that Putin, reportedly a protege of Russia's international debt negotiator Anatoly Chubais, could be placed at the head of the still-powerful FSB. It is possible too that Putin, who as head of the Kremlin's general control department hunted down corruption and profligacy within the government's own ranks, has been made head of the FSB to augment the government's fight against tax evasion and economic crime.


Other commentators said that Kovalyov had made the FSB too independent, and that it no longer acted in conjunction with the government.


"Under Kovalyov, the FSB became less a state organization than its own cooperative," said Yury Korgunyuk, an analyst at the INDEM research institute. "And Kovalyov was a very good cooperative leader. But he tried to do too much, and Yeltsin didn't like that."


Putin, on the other hand, has always been a good performer, he said. "He isn't necessarily a leader, but he does the job he is supposed to do," he said. "Because of that he is less dangerous to the president."


Konstantin Preobrazhensky, a retired lieutenant general in the KGB, said the decision to sack Kovalyov was purely political. "Kovalyov is just as capable to deal with economic corruption as Putin," he said.


"It is unlikely that Putin will make any significant changes in the FSB's activities," he said. "But because he comes from the president's administration, he will be much more obedient to Yeltsin than Kovalyov."


Little is known about Putin's past, other than that he has consistently shied away from the public eye. After graduating from the law faculty of the Leningrad State University, Putin joined the KGB's foreign intelligence administration, which dispatched him to Dresden, then part of East Germany. He served there for about 15 years.


In the 1980's, he became an advisor to Anatoly Sobchak, the liberal head of the Leningrad Soviet, or legislative assembly. In 1991, with the collapse of the Soviet Union, Putin stayed on as aide to Sobchak who by then was the first democratically-elected mayor of the renamed St. Petersburg. From 1994 to 1996, Putin served as a first deputy in the St. Petersburg city government.


When Sobchak was ousted in an election, Putin moved down to Moscow, where he became deputy head of the Kremlin's household affairs directorate, and later, in March 1997, he was appointed head of the general control department and deputy to Kremlin chief of staff Valentin Yumashev.


Liberals welcomed Putin's appointment because of the new FSB chief's own liberal background. But at least one politician was angered by the reshuffle. "Kovalyov was a professional, knowledgeable and reasonable person," Viktor Ilyukhin, head of the State Duma's security committee, was quoted as saying by Interfax. "It is obvious Putin does not have these qualities. He still needs to muster political experience."