Police officials in Prince George's and Montgomery counties are warning officers that a Salvadoran street gang is plotting to ambush and kill them when they respond to service calls.The warnings have been issued based on intelligence gathered from the Langley Park area, a known base for members of the MS-13 gang, officials said. The area straddles two counties.'snip'In July 2002, The Washington Times reported that MS-13 had dispatched about 20 gang members from California to Fairfax County to kill a county police officer at random.There were two confirmed cases in which MS-13 members tried to lure officers behind buildings in...