WASHINGTON, D.C., MARCH 29— Expectations for 2017 have become less optimistic, but the majority of industrial and commercial construction contractors still expect growth this year, according to the latest Associated Builders and Contractors (ABC) Construction Confidence Index (CCI). Although all three diffusion indices in the survey — profit margins, sales and staffing levels—fell by more than five points, they remain well above the threshold of 50, which signals that construction activity will continue to be one of the few significant drivers of economic growth.