In an effort to quell the many rumors circulating regarding the Russian president's physical condition, Kremlin officials reassured the public yesterday that Boris Yeltsin is in good health following his burial. 'Mr. Yeltsin is in fine shape, strong as a Russian bear,' Kremlin information director Vladimir Chernovsky said, standing near Yeltsin's grave. 'In fact, just before dying, Mr. Yeltsin took a long swim in the icy waters of the Volga River, barely tiring at all.' To prove his point, Chernovsky removed the six feet of dirt covering Yeltsin, pointing out his healthy skin tone, hearty frame and barely eaten eyeballs. 