Trying to Prevent the Next Killer Rampage
Police in Ithaca, NY, team up with mental health specialists to halt rampage killings by deranged individuals, spurred by fatal stabbing of Inspector Michael A Padula by Deborah Stagg in 1996; collaboration is hailed by some policing experts, who say it is unmatched elsewhere in country because of focus on pre-empting problems in addition to responding to crises; even Ithaca police officers, initially cynical about approach, now say there has been steep decline in number of chronic callers tying up phone lines and time, and fewer untreated mentally ill people on streets; city has dared to move beyond 'hands are tied' response, emphasizing prevention and devoting police resources to following up on people with chronic problems who do not always want to accept help; photos (M)