International Business Machines Corp. and Fujitsu Ltd. have reached a settlement in their software copyright dispute, the American Arbitration Assn. said. The association, which has been overseeing secret negotiations between the two sides, called a news conference for today. The arbitration group declined to give details on the settlement, and officials of both companies declined comment. The dispute arose two years ago when IBM accused Fujitsu, Japan's largest computer maker, of violating a 1983 agreement involving IBM-developed operating systems, the programs that oversee the internal operations of a computer. Fujitsu makes mainframe computers that run the same software as IBM mainframes. Late last year, Hitachi Ltd., another maker of IBM-compatible mainframe computers, reached a settlement on a similar dispute.