The Maryland Public Service Commission, after receiving hundreds of complaints from consumers, yesterday ruled Chesapeake & Potomac Telephone Co. must have "dial-a-message" vendors play a pre-recorded message warning customers they will be charged for the call.

Many customers did not realize they were being billed for each call in addition to their monthly telephone charges. The calls cost between 20 cents and $1.

Chesapeake & Potomac Telephone Co. began allowing vendors to offer 23 so-called "audiotex" dial-a-message services, including children's stories, sports, and even pornographic messages, in October on the 976 exchange.

The Maryland PSC had not required customers to be informed of the charges until after 200 to 300 customers complained about the charges and -- in some instances -- about the pornographic messages some services carried.

"We felt we had provided adequate information to customers completing those calls," said Web Chamberlin, a C&P Telephone Co. spokesman. "We felt through our media releases that word had gotten out there was a charge, but the commission did feel additional things needed to be done."

As of Jan. 30, audiotex vendors will be required to play pre-recorded messages stating there is a charge for the call.