China's leaders begin a full day of talks with Kim Il Sung today, wielding unsurpassed leverage for dislodging the North Korean leader's nuclear ambitions, say diplomats.The United States and other countries count on China during Mr. Kim's state visit to try to bring North Korea's nuclear program within limits recognized by most nuclear powers. As an ideological bedfellow and aid donor to North Korea, China is in a unique position to make good on several failed international efforts to dampen North Korea's emerging nuclear industry, they say. But it is unlikely China will use its influence fully, they add. "Both North Korea and China are pariah states very much in the cold now - they're each other's best friend - so they don't want to offend one another," says a Western diplomat on condition of anonymity. Kim's visit is part of China's effort to cultivate its relations with remaining communist states since the failed conservative coup in the Soviet Union. Beijing dispatched a top official to Cuba last month and plans to fully normalize relations with Vietnam in November. In order not to antagonize Kim, China is likely just to gently press him on two key bilateral issues: its desire to broaden ties with South Korea, and the imperative that Pyongyang tolerate checks by nuclear inspectors, the diplomats say. Pyongyang recently withdrew an offer to allow officials from the International Atomic Energy Agency to visit its nuclear sites, saying the United States must first remove nuclear weapons from South Korea. Intelligence reports indicating that Pyongyang is building nuclear weapons have kept tensions high on the Korean Peninsula even as the two Koreas have recently taken small steps toward reconciliation. The Defense Ministry of South Korea warned on Sept. 27 that Pyongyang's recalcitrance might prompt it to stage a commando-style attack on nuclear facilities in the north. Ironically, as Beijing declares its long-standing fraternal bond with North Korea, it is engaged in a banner year of trade with South Korea. Bilateral trade is expected to climb from $3.8 billion in 1990 to nearly $5 billion this year, several times the figure between Chinand the north.