SINGAPORE — To judge from the recent exchanges between the leaders of China and Russia, all is sweetness and light in the strategic partnership between the two leading Eurasian powers. But beneath the surface, problems over military sales, trade and energy are weakening Sino-Russian relations just when they appear to be at an apex.

According to the Stockholm International Peace Research Institute, China received 94 percent of its major conventional weapons from Russia in the five years to 2007. They included combat aircraft, helicopters, surface warships, submarines, air defense systems and an array of missiles. Yet in 2007, no new contracts for planes or ships were signed.

Analysts in Moscow say that the Russian-Chinese bilateral commission on military technical cooperation has not met for two years, and that Russia's defense minister has repeatedly postponed a planned visit to Beijing because of a dispute over the supply of Russian heavy-lift transport planes and air refueling tankers to China. Moscow wants the contract renegotiated to raise the price and lengthen the delivery schedule. Beijing has so far refused.