Sears, Roebuck & Co. will introduce its new credit and financial services card nationally months ahead of schedule because test-marketing has been so successful, the company said yesterday. The Discover Card, which combines retail-charge-card features with various financial services, goes on the national market Jan. 23 with a television and newspaper advertising campaign. Sears had planned to offer it nationally in the spring.

"Early results in Georgia and San Diego indicate that consumers are eager to take advantage of the wide range of values the Discover Card offers for individual financial service needs," Edward A. Brennan, chairman and chief executive officer, said in a statement.

Brennan said the after-tax loss of the Discover Card operation, because of advertising and other introduction costs, is estimated to be $115 million in 1986.

"Based on the results we have seen in these pilot markets, we are confident that Discover Card will have a substantial market position nationally by the end of the year," he said.

The card can be used with airlines, hotels, restaurants and other retail establishments. It also can be used as a savings device, with interest based on money market rates, and it provides instant cash access at more than 5,000 locations across the country, Sears said. Sears said other deposit, lending and investment services will be added later. Initially, there will be no annual membership fee for cardholders, Sears said.