* Talk America Holdings of Reston said yesterday it would scale back marketing of its local phone service except where it already has a concentration of customers, and as a result will gain fewer customers than it previously anticipated. Talk America, which resells service that it buys wholesale from regional phone companies at discounted rates, is concerned that federal regulators will allow those rates to increase and make the business unprofitable, said Gabriel A. Battista, executive chairman of the company. The company is scaling back except in states such as Michigan, Illinois and Georgia, he said. It expects to close out the year with 700,000 to 725,000 customers, or roughly 100,000 fewer than it previously forecast. The company said its overall earnings and revenue forecasts remain unchanged.

* ManTech International of Fairfax won a five-year, $20.5 million contract from the U.S. Naval Surface Warfare Center's Carderock division to provide engineering and technical services for submarine and surface ship acoustical trials. Work will be performed in Bethesda and in Panama City, Fla., and aboard ships at sea.

* TeleCommunications Systems of Annapolis said yesterday it converted $15 million of its subordinated debt to equity and raised an additional $10 million by issuing 2.5 million shares of its stock to its institutional investors. TCS, which supplies wireless software and satellite services to government and business customers, did so to reduce its debt, said Maurice B. Tose, chairman and chief executive. The move will reduce TCS's total debt from $26.3 million to $17.3 million.

* PEC Solutions of Fairfax, a provider of public safety software and information technology services, won a contract from Norfolk Southern Railway to provide a new public safety system for its police department. The amount of the contract was unspecified. PEC will provide its computer-aided dispatch system, enterprise information system and field reporting system to support the railway's police operations, including managing emergency response, police recordkeeping, inspection activities and investigations.