The nation's 31 million Medicare beneficiaries paid $2.7 billion in doctor bills over and above the charges the government considered reasonable last year, a citizens advocacy group said Monday.

That breaks down to an average of $38.11 for each of the 70.3 million doctor bills processed by the federal program that included what is known in Medicare jargon as "excess billing."Those 70.3 million claims were 23 percent of the total doctor bills submitted to Medicare in fiscal 1987, the last year for which records are complete.

The excess billing claims came from the 63 percent of the nation's doctors who have not agreed to abide by fee schedules set by Medicare.

Although federal health officials and Congress have instituted a series of programs designed to encourage doctors to follow the Medicare scale, there is no national rule requiring them to do so.

The percentage of physicians who voluntarily follow the Medicare fee schedule ranges from 73.5 percent in Alabama to 14.9 percent in Idaho.

Medicare beneficiaries are required to pay 20 percent of the amount charged even by those doctors who "accept assignment" - that is submit bills that adhere to the Medicare fee standard.