Fidelity Capital, the venture capital division of Fidelity Investments of Boston, acquired a majority stake in Vienna-based Digital Radio Networks L.P., which provides access to credit card authorization services through radio transmissions.

Terms of the agreement were not disclosed.

The Federal Communications Commission permits radio-based credit card authorizations to be transmitted only within a small but strong frequency range on the radio spectrum.

Digital Radio Networks is the only company with a license in that range to provide the service. Other licensee's in the range are companies relying on strong, uninterrupted radio signals, such as utilities and security companies.

Using radio transmission, a credit card authorization takes a merchant about six seconds while conventional methods of authorizing transactions through telephone lines take an average of 25 seconds, said Steward Dougherty, a former employee of Fidelity who is now executive vice president of sales and marketing for Digital Radio Network.

The potential market for Digital Radio Network's technology, mainly high-volume organizations that need the quick transaction time to avoid lines, plus the absence of competition, attracted Fidelity to the company, Dougherty said.

In addition to placing Digital Radio Network's system in high-volume retail outlets, the company will try to tap the cab and limousine markets, he said.

Digital Radio Network's technology is in use in a number of local establishments, including Olsson's bookstores and the parking lots at Dulles International Airport.

Adler Publishing & Communications Inc., Adler Employment Marketing Inc. and Neighborhood Newsstand Inc. merged to form the Adler Group Inc.

Adler publishes a variety of apartment rental and home buying guides and does consulting work in the apartment leasing industry.

Neighborhood Newsstand, which will retain its own identity as a division of Adler, distributes complimentary publications for about 30 organizations in the Washington area.

The merger is part of the company's efforts to create a more focused corporate identity and help with its plans to acquire and start other publications and services, according to a company statement.

Mount Vernon Auto Parts of Alexandria acquired Martin's Hardware of Alexandria to form Martin's Hardware/NAPA Auto Parts. The stores will combine into one location, but will continue to provide all the services they offered independently.

Lafarge Corp. of Reston, a major producer of cement and production materials, acquired the assets of the Davenport Cement Co. and Missouri Portland Cement Co., both of Davenport, Iowa. The acquisition adds three cement plants and 15 cement terminals to Lafarge's 13 plants and 75 terminals in North America.

Innovative Technology Inc. of McLean was awarded a one-year contract by the Library of Congress to provide all federal and military agencies access to the Federal Supply Catalog, a large database of items that have been sold to the federal government.

Softworks Inc. of Clinton entered an agreement with REO Sales Inc. of Alexandria to release a series of real estate software packages. The first edition is a PC-based asset disposition and management package.

GE Information Services of Rockville, a business information systems provider, introduced QuikNews Newsletter, a customized business information service for the telecommunications and microcomputing industries.

The postal barcoding system ACTionMAIL, produced by ACTech of Fairfax, formerly known as Advanced Computer Technology, was approved by the United States Postal Service.

Merrick/Sparrow Advertising Inc. of Kensington changed its name to Merrick Advertising Inc.

Key Financial Personnel and Key Financial Temporaries relocated their Rosslyn offices to Arlington.

Integrated Microcomputer Systems Inc. of Rockville opened a maintenance facility in Rockville to provide maintenance and support services for Zenith Data Systems microcomputers and associated hardware.

Announcements of news and developments affecting Washington area companies should be sent to Regional Report, Business News Department, The Washington Post, 1150 15th St. NW, Washington, D.C. 20071.