At an otherwise lackluster Comdex computer trade show, both vendors and retailers see one ray of sunshine for an otherwise depressed industry.

The bright spot is the development of "local-area networks," or LANs. These are packages of hardware and software that link personal computers into a communicating network able to share information. Just as telephones can carry voices, computer networks carry data, text and graphics.

"By one estimate, only 4 percent of the millions of personal computers installed today are linked into any kind of network. The rest are playing Lone Ranger," said Hewlett-Packard Chairman John A. Young.

The basis for the industry's optimism is twofold: the recent introduction of IBM's long-awaited LAN equipment along with its publication of standards that will allow others to design compatible products, and the growing recognition that communicating personal computers can be more productive than stand-alone machines.

Next year is expected to mark the beginning of a LAN boom in corporate America, many industry officials and observers say.

However, the LAN companies say they will need software comparable to such popular programs as Visi-Calc and Lotus 1-2-3 -- which helped inspire the personal computer boom -- to create a similar surge in sales for LANs.

"The LAN market is going to be driven by software, not the networks themselves," asserts Charles Hart, president of Nespar Systems Inc., a $20 million-a-year California-based local-area network company.

Hart estimates that 80 percent of his company's research and development budget goes into software. "I wish we weren't in the hardware business at all," he said.

The bulk of LAN software focuses on two key aspects of networking: communications and data management.

Nespar includes "electronic mail" software with its system that enables computers on the network to exchange or simultaneously view messages.

Similarly, the "file server" -- the central box which stores the data and controls communications on the network -- can be programmed to make data retrieval easier.

Hart says that companies now are gobbling up LANs to solve specific data-sharing problems. For example, North American Rockwell's purchasing agents now use their personal computers to exchange or retrieve information from the central data base stored on the file server.

Mark Wheeler, a systems and procedures analyst with Hughes Aircraft, said "We expect to double the number of LANs next year. We're working to integrate our big computers with these LANs."

Indeed, says AT&T's Rob Sellinger, a division manager with the company's computer systems, "the trend is toward linking all levels of computing resources in the company."

He points out, however, that the shape of the local-area network will depend on how data is intended to be shared. For example, some file servers will primarily be used to handle communications, shifting data from one personal computer to another. In another situation, personal computers with limited memory capacity will be required to gain access to a file server serving as a central data base.