Twenty-one people were arrested yesterday by Drug Enforcement Administration agents and Seattle police in a major drug bust. A law enforcement source says several are connected to a Seattle nightclub that caters to minors. The defendants have been charged with selling more than 50,000 tablets of Ecstasy, 5 kilograms of cocaine, and a half-kilo of methamphetamines. If found guilty, the defendants face anywhere from 10 years to life in prison. According to a law enforcement source who asked not to be named, several defendants sold drugs at Club FX, an Elliott Avenue West club that plays host to weekend dance parties catering to minors aged 17 and young adults.