The company that is installing a new computerized multiple listing service (MLS) for Northern Virginia real estate agents has agreed to make 110 more phone lines available and modify its software to ease problems that have hamstrung home sales for the last two weeks.

The problems began after Dator Corp. of Greenwich, Conn., installed a new MLS system that began operating July 1.

The MLS system, which replaced a system run by McLean-based Planning Research Corp., allows real estate agents and others in the industry access to more than 100,000 computerized listings of properties for sale or those recently sold in Northern Virginia.

But technical problems, power failures and the fact that many agents were unfamiliar with the system combined to cause an overload. A large number of the attempted calls did not reach the MLS, although Dator did not know how many. Because the MLS system is the agents' lifeline to the real estate market, their reaction to the problems has been heated.

Earlier this week, about 200 angry real estate agents confronted top officials of the Northern Virginia Association of Realtors with their complaints.

"I don't think the system is broken," said Michael Jacobson, president of Dator. "We're going through the shakedown. It's like turning a two-lane country road into a six-lane highway. Everybody knows there's too much traffic on the two-lane road. Once they know a six-lane road is coming, they picture an immediate solution.

"What we do is put up construction roadblocks and make the traffic immediately worse. But once we take down those roadblocks, they have what they want," he said.

Agents are not quite at that point, but they are getting closer. While association officials and some real estate agents said the problems have eased since the Monday meeting, they also said the problems still are hampering their business by making it difficult to get information on homes for sale.

"There's a lot of stabilization that still needs to take place," said Renee Miller, president of the association. The group, along with four smaller boards of Realtors in Northern Virginia that together represent 17,000 members, last January signed a five-year, $15 million contract for the new system.

Herman Methfessel, Long & Foster Realtors' senior vice president and general manager for Virginia and West Virginia, said the problems have hurt his firm's home sales. "People have come up with some ingenious ways to cope {but} I'm sure we've suffered from it," he said. Long & Foster, with 6,500 agents, is the largest realty firm in the Washington area.

While the new system is designed eventually to be faster and easier to use, real estate agents and others can recite a litany of woes that have bedeviled them this month. Some have complained that they are unable to get into the system and that, even if they can, they cannot get the types and kinds of information that they need.

"It's become a meltdown situation," said William Harvey, president of William Harvey & Associates, a Great Falls firm whose 20 appraisers represent about 20 lenders. Appraisers rely on the MLS system to help verify recent home sale prices.

Some real estate agents have complained that they encounter busy telephone signals when they try to get access to the system from their offices. They also complain that the system is slow and that all of the information from the old system has not yet been transferred to the new system. That means that real estate agents have had trouble getting exact information on houses for sale.

The system also is having difficulty accepting changes to sales listings, according to Michael Guthrie, manager of Mount Vernon Realty's Reston office. For example, price reductions aren't showing up for several hours, if at all, he said.

Annette Potts, a member of the Top Producers Club who works at the Annandale office of Coldwell Banker, said the new system is the worst "I've ever used" and that when her assistant tried to revise three listings, it took two hours instead of the usual 15 minutes.

One frustrated real estate agent posted a sarcastic message on the Dator system's bulletin board. While the message began by praising the system -- "I really love this system. It is everything anyone could possibly want," the message ended by saying, "Please address your responses to St. Elizabeths," the D.C. hospital that treats the emotionally disturbed.

To cope with the problems, some real estate agents and firms have taken matters into their own hands. Mount Vernon Realty, with about 3,000 agents, has set up its own database by taking the basic information on homes for sale off the MLS and transferring it to its in-house computer system, which real estate agents can access via personal computers in their offices.

"They can get the real core of the information and then call the listing agent for the rest of the information," said company spokeswoman Judi Lewis.

Agents and others who are familiar with MLS computer conversions say the problems that have occurred are typical of what happens when a conversion on this scale takes place. The association said its MLS is the largest in the country.

"I would say that what's gone on here is fairly typical," said Jim Sherry, president of Jim Sherry & Associates Inc., a Sterling company that specializes in MLS conversions. "The larger the board, the larger the problem."

Long & Foster's Methfessel said, "I've been through a lot of integration and none of them has been smooth as glass. This one is no different."

The problems with the new MLS system have stemmed from a combination of factors, according to those familiar with the system. Problems with the association's four mainframe computers and its operating software meant that the normal transfer of data between the four computers failed to take place when the Dator system first went into operation July 1. At one point, according to one official familiar with the problems, all of the phone lines to the mainframes were going to just one computer, which wasn't working properly.

Also, Sherry and others said power outages caused by recent thunderstorms delayed the transfer of data from the PRC system to the Dator system and knocked out more than 100 phone lines that connected real estate agents to the system.

Officials are now turning their attention to problems with the 4,300 terminals used by real estate agents. Sherry said there are more than 100 types and brands of terminals being used and some types of machines are having compatibility problems. In some cases, Dator is sending technicians to fix the problems.

Last, but not least, there is the problem of training. A Dator official said that more than 10,000 people attended training sessions, which were held beginning in May, to learn how to operate the new system. However, that leaves almost 7,000 people now struggling to learn the new system.

"They're not employees where you can say, 'You report to class Monday morning,' " said Sherry. "These are independent contractors -- and independent is the operative word."

Once the system is fine-tuned, officials say it will offer extensive new features for real estate agents, as well as for home buyers and sellers. Real estate agents will no longer have to memorize arcane codes to operate the system. Among the added features is a message function that will allow real estate agents to exchange electronic mail.

Home buyers and sellers also will be able to get more attractive, readable MLS reports, and the system allows agents to customize sales analysis reports to individual buyers and sellers. Agents also will be able to get access to their personal information from offices other than their own.

In the meantime, Dator officials are unable to say when the system will be running smoothly. "If you ask me, as president of the association," said Miller, "it better not take long."