Thousands of individual subscribers to Blue Cross and Blue Shield of Maryland will begin receiving state-ordered refunds in September in the form of credits to their quartery bills, a spokesman for the insurance companies said this week.

The refunds were ordered by the Maryland insurance commissioner after Blue Cross and Blue Shield financial statements for 1977 showed surpluses in their reserve funds. Some $15 million in overcharges were ordered returned in an action that affected more than a million policyholders.

In November, group policyholders will begin receiving rebates in the form of checks, said Nicholas Greaves, a Blue Cross-Blue Shield spokesman. He said $13 million of the $15 million ordered returned will go to 10,000 group subscriber might get has not yet been determined.

"That will depend on the size of the group and the amount it contributed toward our financial gain in 1977." Greaves said.

The rebates for individual subscribers will range from $3.25 to $46. Greaves said, depending on how comprehensive a policy the subscriber holds.

The insurance companies had until July 31 to decide on a distribution plan for the rebates. The plan submitted to the state this week must be improved by Maryland Insurance Commissioner Edward J. Birrane Jr., who issued the refund order July 15.

Greaves said the distribution plan leaves it up to the firms that offer group policies for their employes to determine how the rebate will be distributed among the individual members of the group.

No refunds will go to federal employes covered by Blue Cross-Blue Shield because federal groups have a refund clause written into their contracts with the insurance companies.

Greaves said the insurance companies came up with surpluses in their reserve funds because their policyholders used less of the insurance funds they had been anticipated and because of the moderation of increases in hospitalized costs and the cost of medical services.

Blue Cross, which covers hospital expenses for subscribers, and Blue Shield, which covers doctors' bills, maintain reserve funds to protect them in the event of a disaster that would result in numerous claims at once.