When Jeff moved into a group house in Mount Pleasant, his housemates thought he would be perfect; he was clean, conscientious and financially stable. But once Survivor magazines and "How to Kill" parts I, II, and III began appearing on the coffee table, they became worried. When they got a load of his high-powered gun collection, they threw him out.

As the cost of housing rises, more and more Washingtonians are turning to group houses as an alternative to single house or apartment living. But like any situation combining human emotions, eccentricities and money, there are sure to be a few short fuses.

Enter housemate services; these ultimate see-the-need, fill-the-need enterprises have cropped up all around the area to match up Washington's population; not to date but to live together -- an often longer-lasting and more intimate affair.

Betsy Neal, director of Roommates Preferred, says her service is for those who would prefer not to pin a sign to the wall of an ice cream store or bagel place. "It's for people who care about who they are bringing into their home."

"It's so hard to judge someone in one short interview," says one housemate of Jeff's who wishes to remain unidentified. "Having a service to screen out these people a bit is a small price to pay for your sanity."

For $50 (nonrefundable), Neal meets individually with those looking for a home (searchers) or a representative of a group house (providers) and dishes out names and phone numbers of prospective housemates until they meet their match. "This way my clients get a certain group of people -- the kind who will take the time to come to our office and chat a bit."

Once the housemate has moved in, she gives her client a two-month trial period during which he or she can use her services again if things don't work out. "My clients come to me because they don't have time to interview, nor the inclination. They have some sort of sense about whom they want to live with and how they want to live, so they come to me. And by that time they've taken a lot of the chance out of it. It's a pretty sure thing that it's going to work out."

Inge Hyder of Roommate Referrals in Columbia, Md., advises prospective housemates not to dive into something when they are feeling desperate. "You can tell a lot about a person if you keep your mind active. But at this time your mind isn't working right." That's why an objective third person, she says, is helpful.

Hyder, who has been covering Columbia, Silver Spring, Laurel and Olney for the past 10 years, charges searchers $60 (and offers a one-month trial period), payable after a no-obligation interview. Providers pay $40 at the beginning, the balance -- $20 -- is payable when a housemate moves in.

Computer assisted, she can work out details concerning who smokes, who has children or pets, and room sizes -- "things that are important for these people." She's made some wonderful matches, she says. "People who have remained together for five and eight years."

Bob Kolacki, an engineer with the Navy, matches housemates in Northern Virginia part-time, helping around 20 people a month. He tries to screen out improbable matches before charging a client $25 for a list of names. He then requires $15 once the client moves in.

"I can't guarantee a person's background but I do try my best to make sure they're legitimate."

When Louise Ramsey created Room Finders in Annapolis two years ago, she thought her clients would be mostly young professionals in their early twenties. They have turned out to be only 35 percent of her client base. "My clients' ages range from 18 to 80," she says. "I deal with professional, blue-collar, single parents, both male and female. One woman said to me 'I'm looking for a "Kate and Allie" situation.' I even helped a woman who had three kids and a dog."

Ramsey now finds herself covering all of Anne Arundel County as well as Prince George's County. Housemate services are helpful, says Ramsey, because classifieds don't tell you enough about a person. "You can't tell what their habits are ..." And many of Ramsey's clients are women who don't want to advertise for fear of obscene phone calls. "Even men can't be bothered with the phone ringing at 3 in the morning. It's a big safety concern."

When interviewing a prospective housemate, Neals gets a feel for the client by chatting about topics unrelated to roommates. Then come more direct questions about smoking, room sizes, cleaning habits. "My phrase is always, 'Is your cat declawed?' "

Once the phone call has been made and you find yourself on a prospective house's front stoop, Neal suggests that the main thing to remember is to be yourself.

"If you go to a job or to a party," she says, "you have to perform different roles in different places. But every one has to be themselves some place, and that's where you drink your orange juice in the morning."

Talk, she advises, about life's little habits. "People can be on the opposite ends politically, can come from different backgrounds, have different groups of friends, but it's life's little habits that will spell disaster. If three people have to take a shower in one bathroom at the same time, it won't work. If someone likes to wake up at dawn and another stays up all night, it won't work."

Find out, above all, exactly what their home means to them. Is it a retreat from the rest of the world or is there an open door with friends dropping in unannounced all the time. Do they give small dinner parties or large impromptu keg parties? Are they looking for someone to socialize with or someone who is completely independent?

Kolacki strongly suggests that they arrive at the house alone. "One of the big fears in a group house is lack of space. If a woman shows up with a boyfriend in tow, they are going to assume he's going to be around all the time."

On the side of the providers, Hyder recommends that they check references and make sure they procure a security deposit or the first month's rent in advance.

The idea, says Neal, is to be as comfortable as you would with a family. Although money plays a big role in deciding to enter a group house, the sense of family, security and friendship that evolves can lull a person into staying much longer than expected.

"People like to share, like to have other people around." Through roommates, she says, you can meet other kinds of people, with different view points. In mixed houses, many form purely platonic relationships with those of the opposite sex for the first time. "You become a family of sorts, it's a support system. And there is always someone to say hello to at the end of the day."

In addition to these for-profit organizations there is Operation Match, a government-funded housing referral service, located in D.C., Alexandria and Falls Church, as well as Montgomery, Fairfax, Arlington, Loudoun, Prince William and Prince George's counties, that finds housing for free.

"We have no limitation on income, says Harold Valentine of the D.C. office. "In fact, we get a lot of referrals from for-profit organizations." Operation Match, he says, often handles exchanges where a resident will offer a room in exchange for company or maid/yard help. "I've matched people with no income."

Neal says the nonprofit referral services and those for profit tend to deal with different clients. "I usually deal with just housing needs where the clients have their own jobs, not exchanges of room and board for work."

Both, however, help to make better use of Washington's limited housing. "There is great frustration out there," says Valentine. "We try our best to make everyone compatible."

"After all you're talking about people you're going to be living with," says Neal. "It's very personal."