MANILA, Philippines — American and Filipino security officials have agreed to keep a U.S. mid-range missile system in the northern Philippines indefinitely to boost deterrence despite China's expressions of alarm , two Philippine officials said Wednesday. The U.S. Army transported the Typhon missile system, a land-based weapon that can fire the Standard Missile-6 and the Tomahawk Land Attack Missile, to the northern Philippines as part of combat exercises in April with Philippine troops and to