In a housing market plagued by falling sales and rising interest rates, the Washington Board of Realtor's new computer home-listing service has reportedly malfunctioned or been out of service every day since it was installed in February. Disgruntled agents, who describe the problems as "serious" and "abnormal," have demanded that the system, which lists units for sale in the District, be fixed immediately or replaced.

Some agents and brokers said this week that service to their clients during the crucial spring sales period has been severely hampered by system failures. About 40 agents filed a complaint with the board last month asking for a resolution of the problem.

Washington Board of Realtors president G. V. Brennerman refused to comment this week on the situation and expressed regret that board members felt it necessary "to go public" with their concerns about the service.

Other computerized multi-listing services--known as MLS systems--are maintained by the boards of Realtors of Montgomery and Prince George's counties and Northern Virginia. Officials of those boards said they occasionally experience minor service outages, sometimes due to weather conditions that affect telephone connections between office terminals and the main computers. About 60 of the 212 terminals in the District system are used by Realtors in the suburbs, who have also been blocked from getting D.C. information recently.

"We had a computer system that worked," said Norma J. Gordon, an agent with Leigh and Schwab Inc., referring to the Washington board's original multi-listing service installed in 1978 and run by PRC Realty Systems of McLean. PRC's contract with the Washington board expired Feb. 22 when the new system was installed by Realtron Corp. of Redford, Mich. "What we have now is a system that absolutely won't work," Gordon said.

MLS data on local real estate transactions is considered an important selling tool by most agents, who use the information to determine housing availability and sales trends of comparable homes. "Multi-listings are vital," said Vivian Ray, an agent with Begg Inc.

PRC has run Prince George's MLS system since 1973, when the firm acquired Realtronics of Denver, the county's original MLS vendor. Northern Virginia's board switched from Realtron to PRC in 1976. Montgomery County began its service with Realtron in the late 1960s and switched to PRC in 1977 before creating its own in-house system in 1979.

Peter M. Jacula, director of the Northern Virginia board's MLS operation, said he is "generally happy" with the PRC system, but "we gripe occasionally" about speed and outages. "When we first came on-line with PRC, service was terrible," he said, noting that it took "a while" to educate users and sort out technical problems.

Jacula said PRC's McLean location was a key factor in the changeover from Realtron, which is based in a Detroit suburb and has its main computer in Pompano Beach, Fla. PRC also provided faster service, he said.

William C. Stuart, a partner in the Stuart and Maury brokerage and chairman of the Washington board's MLS committee, said he knows "there have been problems" with the Realtron system: "I'm aware there are people who are not satisfied. We're evaluating the problem" to determine the next course of action.

Stuart said the situation involves "many factors," including possible system inadequacies and complications caused by users of the new, expanded service who have not been trained properly.

Realtron vice president Rex Marr acknowleded "deficiencies in the system," noting that Realtron employes have been working since December to iron out "bugs" in the service and to instruct users about the computer programs and equipment.

Marr said Realtron's Washington service is "revolutionary," containing data by square and lot numbers for every piece of real estate in the District. Most MLS systems, including some run by Realtron, only list properties that have been filed individually by users, he said. Washington's first system provided short lists from about 3,000 user-entered items, while the new Realtron service includes about 130,000 entries, he said.

"We went out and visited about 180 offices" to teach agents and brokers how to use the system, Marr said. Some of the meetings "turned into gripe sessions," he said, with a lot of complaints about the system's slow speed.

"The larger database would slow it down," especially if an information request is made using incorrect computer commands, Marr said, adding that some agents have told him "they don't need that much data." He said that board officials specifically asked for an expanded database.

In addition to problems caused by users, the system has been malfunctioning because of faulty programs and equipment--known as software and hardware, respectively, Marr said. He added that all of the problems are start-up difficulties often encountered during installation of computer systems.

Ed Keller, Realtron's technical director, said Realtron uses a different computer language than the PRC system, a change that has confounded many agents. While the abbreviation "ST" meant "street" in the PRC system, it means "soil type" to Realtron, he said.

"We install on the heels of other vendors and we know how traumatic a change can be," said Sharon Hox, vice president of PRC's customer services division. She said her firm has been asked by the Washington board to quote new contract terms and to determine how quickly a return to the PRC system could be effected.

"We do not believe that the general membership of the Washington board was involved in the decision to switch" from PRC to Realtron, she said, because many agents expressed surprise when PRC service representatives informed them of the changeover. "Some of the membership may believe that they didn't have a chance to have their say."