President Clinton began an international phone campaign against North Korea by dialing up Russia's President Boris Yeltsin. Next on Clinton's call list: China's President Jiang Zemin. The U.S. campaign to secure passage of U.N. sanctions against North Korea continued to prompt Pyongyang reaction. The latest: North Korea pulled out of the U.N. nuclear watchdog agency. South Korea responded to the rising tensions by calling up 6.6 million reservists.