The Chinese government has begun playing a more active role in pushing the United States and North Korea to settle their differences over the North Korean nuclear development program, according to Chinese government and Western diplomatic sources.

In a series of moves aimed at influencing both sides, the Chinese government has warned North Korea to stop provoking the United States, backing up the warning by closing an oil pipeline to North Korea for three days in late February, the sources said. At the same time, China has blocked U.S. attempts to use the U.N. Security Council to censure North Korea for withdrawing from the nuclear Non-Proliferation Treaty, and has announced that China opposes sanctions against North Korean leader Kim Jong Il.

"We have realized that we cannot let this situation alone," said a Chinese government official involved in foreign policy. "So we've decided to attempt to influence it, specifically by getting the two sides together." To that end, he said, China has transmitted more than 50 messages between Pyongyang and Washington. It also has held numerous meetings with diplomats from both sides. Government sources said a Chinese offer to host talks between the two sides still stands.

The initiatives are a result of a realization among senior Communist Party officials that unless Beijing begins participating in the search for a solution to the Korean crisis it risks losing influence in an area vital to its security, Chinese officials and scholars said.

China had been slow to react to the North Korean-U.S. dispute during the country's political transition last year. The 16th Congress of the Communist Party took place in November and it wasn't until then that President Hu Jintao, Vice President Zeng Qinghong, and Foreign Minister Li Zhaoxing were assured of their positions.

Hu Jintao underscored a more active Chinese role in the North Korean-U.S. dispute on March 16 in his first phone call to President Bush, shortly after his formal election by the rubber-stamp National People's Congress. Officials here said Hu urged dialogue with North Korea "as soon as possible."

There is some concern that the North Korean government may escalate tensions while the United States is preoccupied with Iraq by resuming test-launchings of long-range missiles, analysts here said. The North Korean government claims the right to develop missiles, and has fired two short-range missiles off its east coast in recent weeks. The Bush administration, for its part, could begin to impose sanctions against North Korea, something Beijing believes could also lead to a showdown.

China is concerned that once the Bush administration ends the war with Iraq, it will turn its attention to destabilizing North Korea -- another of the countries, along with Iran, designated by President Bush as part of an "axis of evil." That likelihood was highlighted in a series of articles co-authored by leading academics here, Piao Jianyi, Zhang Liangui, Jin Xide, and Zhang Tuosheng, in World Affairs magazine on March 16.

The scholars, who also function as government advisers, wrote that the Bush administration is not willing to adopt a solution similar to the compromise worked out by the Clinton administration in 1993-94 in which North Korea agreed to end its nuclear program in exchange for fuel, food and a light-water nuclear reactor. The scholars argued that the prevailing view in Washington tends to support the overthrow of Kim Jong Il rather than the continuation of the status quo on the Korean Peninsula.

If North Korea obtains nuclear weapons, the United States would "destroy North Korea and destroy the Kim Jong Il regime," wrote Zhang Liangui, in one of the articles. If the situation eases, the United States still would "first resolve the nuclear issue and then settle the Kim Jong Il regime."

Kim's ouster, the essays argued, would be disastrous for China, sparking a mass exodus of refugees, cutting off South Korean investment in China and removing a useful buffer state between China and South Korea, where 30,000 U.S. troops are stationed.

The essays had been circulated among high-ranking party officials and helped change the way the leadership viewed the crisis, Chinese sources said.

"There is a realization now that we cannot expect the United States to act like it did in the past," one Chinese source said. "As a result, we have to protect our interests. We have to act."

Another reason for Chinese concern involves the fact that more than one million Chinese died to protect North Korea during the Korean War. There are deep ties between the two countries, especially between China's People's Liberation Army and North Korea's forces.

In mid-February, Chinese Vice Foreign Minister Wang Yi met North Korean Foreign Minister Paek Nam Sun in Beijing and told Pyongyang to stop "playing with fire," a Chinese source said. Wang did not threaten to use sanctions against North Korea, he said, but Wang made it clear that China wanted to begin to move the crisis toward a resolution.

Some time after Feb. 18, sources said, China closed the pipeline from the Daqing oilfields to North Korea for three days. China explained the move to North Korea as a technical problem but "Pyongyang didn't believe us," said a senior Chinese scholar with knowledge of the action.

China has used technical glitches to explain such pressure tactics before. In November, China suspended rail service with landlocked Mongolia for two days while it hosted the exiled Tibetan spiritual leader, the Dalai Lama, who Beijing views as a separatist.

Chinese officials said Beijing was also blocking U.S. efforts to squeeze Pyongyang. For months, China has not cooperated with U.S. efforts to use the Security Council to formally criticize North Korea for abrogating the nuclear Non-Proliferation Treaty. The United States wants the Security Council to issue a formal rebuke by April 10, the day North Korea's departure from the treaty becomes official. But China is not participating in any meetings to draft a statement, Western diplomats said.

China worries that such a move could further alienate the already prickly regime in Pyongyang and that the Bush administration would follow a statement with sanctions, officials said.

"Sanctions will not do, and we are opposed to the wanton use of sanctions or the threat of sanctions," Foreign Ministry spokesman Kong Quan said last week.

South Korean soldiers stand guard on a road near the demilitarized zone between North and South Korea.