Government Employees Insurance Co. yesterday implemented new automobile insurance rates in Maryland that will increase premiums by an average of 9.8 percent.

The insurance company, the largest insurer of cars in the metropolitan area, was granted an increase in rates -- varying according to automobile, location, use and other criteria -- in a decision last week by the Maryland Insurance Division.

The Washington firm traditionally leads other insurance companies in boosting rates, so requests for higher rates from other companies are expected, a Geico spokesman said.

The rates became effective yesterday and will not apply to current policyholders until their policies are renewed. Geico's last automobile insurance increase, last October, averaged more than 10 percent.

Since 1977, Geico's premiums have increased by a total of 21 percent, including the recent hike. The consumer price index in Maryland rose by 34.2 percent during the same period, a Geico spokesman noted.

The rate increase was requested by Geico last April and was based on increases in medical care and vehicle repair costs.

Under the new rates, the adult driver of a 1979 Chevrolet Impala in Montgomery County who drives only for pleasure with required and full comprehensive insurance coverage will pay $330 a year, up from $300 previously. c