Ten real estate firms and five of their officers were indicted last week by a federal grand jury in Syracuse, N.Y., on charges of conspiring to fix brokerage commissions in the sale of residential property in Onondage County.

A similar case is pending against six major realtors in Montgomery County.

The criminal indictment alleges that the realtors had "a continuing agreement, understanding and concert of action . . ." to "fix, raise, maintain and stabilize commissions." The result of the scheme was to set commissions at artificial levels, which effectively eliminated price competition, the court document charged.

The percentage amounts of commissions were not given. However, their gross commissions from 1972 to 1974 are said to have amounted to approximately $4 million on sales of $60 million, or 6.5 per cent. The defendants were charged under the Sherman anti-trust act after it was found that the 10 companies accounted for nearly 75 per cent of the total residential sales processed through the multiple listing service.

If convicted, the realtors face maximum fines of $50,000 and a year in prison each; their firms could be fined a like amount. A companion civil complaint requests the court to bar them from continuing or renewing the alleged conspiracy to fix commissions.

The Greater Syracuse Board of Realtors was named in the action, as well as the following companies: Gallinger, Eagan, Menter, Clark, DeWitt, Blatchford, Longley-Jones, Marshall, and Olson-Peck, along with some of their officials. Two other former realtors were also indicted.