Afghan President Hamid Karzai has infuriated international observers by failing to crack down on corruption and for sanctioning an allegedly rigged election. But United Nations officials are cautiously optimistic about his newly announced cabinet, which jettisons two of his most controversial members. ''Early indications are encouraging for some of the key ministries,'' Aleem Siddique, a U.N. spokesman, told the Associated Press, without naming specific choices. ''The U.N. has made clear that we need to see more reform-oriented ministries and of the names we've seen, we're seeing a step in the right direction." One of the removed cabinet members is Muhammad Ibrahim Adel, current minister of mines, whom U.S. officials have alleged took $20 million in bribes to steer a $3 million contract to a Chinese company.