Picking a specialist for a delicate medical procedure like a heart bypass could get a lot easier in the not-too-distant future. The government announced Monday that Medicare will finally allow its extensive claims database to be used by employers, insurance companies and consumer groups to produce report cards on local doctors and improve current ratings of hospitals. By analyzing masses of billing records, experts can glean such critical information as how often a doctor has performed a particular procedure and get a general sense of problems such as preventable complications. Doctors will be individually identifiable through the Medicare files, but personal data on their patients will remain confidential.