Alienation Is a Partner for Black Officers
Ongoing special report, Blues, on failure of New York City Police Department to diversify ranks with more blacks in frontline positions, one of its most important personnel objectives; difficulties in integrating ranks are tied to larger social forces, including competition for finite population of qualified black men from private business, but to blacks in uniform one of department's deepest problems is department itself; wide variety of black officers and detectives say department has struggled with integration in part because of bungled recruiting efforts, insecure commitment and promotion rules that leave few black men at top; say problems are compounded by type of aggressive policing that led to shooting of Amadou Diallo in 1999 that tends to cement its poor reputation among young blacks it most hopes to recruit; aggressive tactics, heralded by Mayor Rudolph Giuliani and police officials as prime factor in city's crime decline, have eroded morale and enthusiasm of what is perhaps greatest asset in diversity recruiting efforts, namely, black officers; photos (L)