(28 Aug 1997) Mandarin/Nat Central America became the latest battleground between China and Taiwan on Thursday. Beijing asked Panama Thursday to retract an invitation to Taiwan's President Lee Teng-hui for fear that the trip would assist the cause for Taiwanese independence. Lee is planning to attend a conference on the Panama Canal on September 7-10. Taipei views international ties as its best counterweight to China's insistence on reunification, but Beijing is determined to keep Taiwan