KUWAIT CITY - Sheikh Jaber Al Ahmed Al Sabah, the emir of Kuwait, returned Tuesday, after months of treatment and rest in the United States and Switzerland. Sheikh Jaber, 79, spent more than two months in the US, where he had medical tests and surgery for a dilated blood vessel in his left leg. He then moved to Zurich, Switzerland, for recuperation.He has made few public appearances in recent years. Whenever he did appear, he spoke with difficulty and relied on support from his aides. With the crown prince, Sheikh Saad Al Abdullah Al Sabah, also ailing, Sheikh Sabah Al Ahmed Al Sabah, the prime minister and the emir’s half brother, seems to be the most likely candidate.