The Maryland Public Service Commission yesterday approved a series of rate changes by Bell Atlantic-Maryland that will raise the cost of its "call waiting" service by 50 cents a month and cut the cost of telephone calls to certain parts of the state and other services.

The five-member commission approved the changes with no discussion at its administrative meeting yesterday. Such alterations, which involve services that are considered subject to competition or do not increase revenues to the company, can be made without detailed proceedings, according to Paul Buckley, the acting People's Counsel, the state official that represents ratepayers before the Public Service Commission.

The changes are effective tomorrow.

The cost of call waiting -- which signals a person using a telephone that another person is calling -- will go from $3.50 to $4 a month. "Our studys show customers expect to pay that or more for the service," said Bell Atlantic spokesman David A. Pacholczyk. "The service has value."

But for those customers moving their phone to a new address, adding a line or another service, the processing fee will be cut from $16 to $5.