BLOOMFIELD - A generation ago, Bloomfield was heralded as the all-American community. Blacks and whites lived side by side, chasing the American dream of middle-class stability without regard to skin color. There were trimmed lawns and good schools. Now, Bloomfield operates one of the most racially segregated school systems in the state. Minority students, mainly black children, account for 95 percent of public school enrollment. And when results were released recently on the state's annual 10th-grade achievement test, this quiet, middle-class suburb found itself confronting a question more often associated with the nation's poorest urban school systems: