KHMER ROUGE FORCES halted a major drive by Vietnamese and Cambodian government troops, which have now shifted north to face less formidable non-communist groups, resistance radio and officials said Tuesday. . . . TAMIL GUERRILLAS triggered a remote-control land mine under a jeep carrying Sri Lankan security personnel, killing nine policemen who were returning from a hospital in the country's northwest. . . . GERMAN CHANCELLOR Helmut Kohl will fly to Washington on May 20 for a two-day visit, during which he will hold talks with President Bush.