Maryland Insurance Commissioner Edward J. Muhl reduced by about one-half yesterday the health insurance rate increases requested by Blue Cross/Blue Shield.

Under rates approved by Muhl, premiums for standard family policies will go up 10 to 20 percent, depending on the type of policy.

Persons insured through employe group health plans are not affected. Rates for those policies go up on a different schedule, depending on when the employer's policy is renewed.

In reducing the request, Muhl ruled that the insurance company overestimated a likely increase in health care costs. Part of the request also was based on an expected higher federal tax bill, and on added expenses incurred during the past few years. One such expense, for example, resulted from the consolidation of Blue Cross/Blue Shield, which used to be separate companies.

But Muhl reduced the importance of those factors in determining the increase.

A typical family insured by a Blue Cross/Blue Shield standard health plan now pays $1,109 in annual premiums, whether the policy was underwritten or converted from a group plan.

After the increase, families on individually underwritten standard plans are to pay $1,221.64, up 10.2 percent; families with the converted standard policies are to pay $1,336.60, a 20.5 percent increase.