MCALLEN - A late-night tip led U.S. Border Patrol agents to five rooms at the Matador Motor Inn, where human smugglers had abandoned 22 men from China. Although the Chinese nationals were economic migrants, their discovery Aug. 16 in downtown McAllen left many with an uneasy feeling. If a large group of men seeking work could be moved across the Rio Grande undetected, why not a squad of terrorists? ''It sure does worry me," said Estella Castillera, whose in-laws own the motel. Although she considers it unlikely terrorists could cross the Texas border, she carefully adds, ''Let's hope not." The...