The American Electronics Assn. estimated that there were 2.52 million domestic electronics employees in September, 1986, compared to 2.54 million at the start of 1986 and 2.56 million in September, 1985. In the first nine months of last year, the association said, employment in the computer segment dropped 3%, or 16,000 jobs, while semiconductor employment increased 0.3%, or 900 jobs. Software-programming employment rose by 5.2%, or 10,000 jobs. The figures are subject to revision, the association added.