Cities and towns could be forced to sue their own residents, eliminate life support services, and pay higher health care bills unless the Legislature reins in an attempt by health insurers to slash ambulance costs, said lawmakers, fire chiefs, and municipal officials yesterday. “We’re not asking for a handout, we never are. We’re asking for a fair deal,” said Mayor Robert Dolan of Melrose, speaking at a State House press conference. “All we ask is not to be victimized by needless cost-shifting by Blue Cross Blue Shield.” At issue is a practice recently implemented by Blue Cross Blue Shield of Massachusetts intended to cajole ambulance providers to join the company’s contracted network: Rather than pay for ambulance services provided by out-of-network companies, Blue Cross will cut a check to patients for the cost of their ambulance ride. That would leave it up to the ambulance companies to seek out their patients and collect the check.