WASHINGTON, Sept. 28 — An internal assessment by the Defense Intelligence Agency has concluded that most of the information provided by Iraqi defectors who were made available by the Iraqi National Congress was of little or no value, according to federal officials briefed on the arrangement. In addition, several Iraqi defectors introduced to American intelligence agents by the exile organization and its leader, Ahmad Chalabi, invented or exaggerated their credentials as people with direct knowledge of the Iraqi government and its suspected unconventional weapons program, the officials said. The arrangement, paid for with taxpayer funds supplied to the exile group...