Like other fields in which access to timely information is vital, the real estate business has gone through a computer revolution.

To survive, larger real estate firms say they must have access to the computerized multiple listing services run by local boards of Realtors. Discount and cut-rate brokers who have been shut out of these computerized listings -- when other Realtors objected to their commission rates -- say their business has suffered. And, increasingly, as national companies absorb independent local firms, access to nationwide, computerized listings for homes have become vital.

As broker dependence on computers has grown, so has the business of Planning Research Corp.'s Realty Systems unit, a 12-year-old subsidiary of the Washington company that has helped put computer listings in the hands of thousands of agents across the country. The company claims to serve about a fifth of the nation's real estate firms. About a third of the industry uses computers.

The success of the PRC real estate subsidiary has been so dramatic that the company's management is thinking about easing its long-standing dependence on government contracts and moving more aggressively into commercial business.

In the last fiscal year, the subsidiary had the largest profit of any PRC arm in history; the company says it has now cornered about 60 percent of the computerized real estate listings market, despite the competition of such national firms as American Broadcasting Companies Inc. and McGraw Hill Inc.

"PRC's role, in effect, has been to lead the way," brags Bert Helfinstein, president of the McLean-based PRC Realty Systems. "We convinced the real estate industry that computers are a viable tool."

In 1973, just after PRC got its operation going in earnest, the company reported sales of about $300,000; the next year, it was $1 million. By 1980 it was nearly $40 million.

Using about 100 PRC computers scattered across the country, the network of brokers hooked into the PRC listing system connects realty boards in 106 cities and includes major parts of suburban New York and the Los Angeles metropolitan area.

In the Washington area, realty boards in every major jurisdiction in the Washington area except Montgomery County use some form of PRC services. The Montgomery County Board of Realtors was a PRC customer, but decided more than a year ago to set up their own computer system.

Using equipment from Hewlett Packard Co. and Texas Instruments Inc., PRC put together a computerized system that permits agents to get a wide variety of data about their local real estate market.

Multiple listing services, frequently subsidiaries of regional real estate boards, contract with PRC to offer their members listings of houses for sale. A firm that sells another company's listed house splits the commission with the originator.

Until the adaptation of computers to the real estate business, these listings were often mimeographed, limiting the agent's ability to provide up-to-date compilations to available homes and their prices.

But the PRC system, described by the firm as the first successful computerization effort in the real estate industry, can provide an agent with an array of information, including an assessment of recent housing prices in a particular region, dating back as far as a year or more, a PRC spokesman said.

Potential home buyers are asked to fill out a standardized form listing the features they are looking for, such as the type of fuel or financing they want to use.

The printer in the agent's office then matches the available housing units to the buyer's specifications.

Computer hookups also allow the agent to make quick financial calculations and a survey of the market at large.

PRC has also become a publisher of house-listing books, which are printed at four sites across the country, including one in Fredericksburg.

Helfinstein contends that the system is cutting down on the time needed to sell houses. He said one study of the Memphis market, for instance, indicated that houses were on the market an average of two months after computers were introduced, down from an average of three months.

"It's a matter of productivity," Helfinstein said. "And productivity is important because business has been so bad that a lot of real estate firms have not been able to meet expenses."

PRC took off after it bought out a struggling concern, Realtronics, in 1972, when the PRC Realty operation was four years old. That purchase came at a time when the National Association of Realtors was failing in an effort to bring computers into the hands of agents.

"We learned a lot from the old system," Helfinstein said. Among the keys to PRC's success was its ability to create a simple system with a variety of options for the agents, he added. "We knew we had to build a system that would be simple enough to appeal to the majority of real estate firms."

PRC staffs its McLean control center 17 hours a day, has service representatives on call 24 hours a day and has spare parts at four locations around the country to prevent extended periods of computer "down time."