Caught between the rising cost of buying a home and the declining amount of rental housing in the Washington area, more and more groups of unrelated people here are pooling their resources to rent single-family homes.

This trend, which began a couple of years ago, is likely to acclerate as home prices continue to soar and apartments remain in scarce supply.

Two other factors that seen to be pushing groups into single-family houses are the conversion of former low-rent apartments to condominiums and the demise of rooming houses.

Two other factors that seem to be pushing groups into single-family houses are the conversion of former former low rent apartments to condominiums and the demise of rooming houses.

For many years rooming houses were quite numerous in our East Capitol Street neighborhood and along the other main streets which were served by the old Capitol Transit street cars. For the single person in Washington, the "Rooms for Rent" and "Room and Board" signs meant inexpensive and simple accomodations. This is the same sort of living that single people are seeking today when they form groups and rent single-family houses.

Limitations on the number of unrelated individuals that can be in a group renting a single-family house vary in the different local jurisdictions. In Arlington and Fairfax the limit is four, in Montgomery and Prince Georges its five, and in the District the limit is six.

Whatever the reasons, for the landlord this shift is the rental market brings both advantages and problems.

The primary advantage is that is is now easier to find a tenant for a house in what used to be the "off season " for rentals -- from September to May, when children are in school -- than was the case a decade or so ago.

At the same time, it may be more difficult for a landlord to determine whether a group of unrelated people -- as opposed to a family -- will be responsible with the home and reliable about paying the rent. For one thing, there almost always are more than two wage earners to evaluate, and the life expectancy of the group itself also becomes an issue. In terms of stability, groups can range from granite to quick sand. Usually groups fall into one of the following categories:

Those with a good "track record": Either the entire group, or two or three of its members, have lived together for a year or two and have adequate incomes and a satisfactory financial history. These groups generally make good rental prospects.

Newly formed groups: Since they have no previous history as a group, the landlord generally wants to get detailed information for the past two or three years on employment and bill-paying and renting record of each member of the group, and this can get to be a complicated process.

Landlords looking for evidence of a group's cohesiveness can take heart if two of three members work for the same firm or are employed in the same or related lines of work or come from the same hometown or college.

Often the only thing a new group has in common is the desire to jointly rent a place to live. Such groups are likely candidates for sudden disintegrtion and can make poor tenants.

Full-time undergraduates. They usually coalesce into groups in the late summer and early fall and beat the bushes for off-campus housing. As a general proposition, they are short on cash. They might not be as reliable as other tenants, both because they can get so wrapped up in their individual activities, academic and otherwise, and because often they are short-term renters who aren't as likely to care about upkeep of the property.

Many landlords and rental agents have modified their procedures to accomodate the new trend to group rentals.

For example, it is quite common now for leases for group rentals to specify that all adult members of the household be listed by name. Except for the signature of husband and wife, leases for families usually just specify the number of occupants and whether they are children or adults.

Also quite common is the requirement that any changes in the occupants, even if the total remains the same, must have the prior wwritten approval of the landlord or his agent. This is a tightened variation of the usual requirement in leases to families that no portion of the premises may be sublet without the written consent of the landlord.

Coming into increasing favor is the practice of having each adult member of the group not only fill out an application but also sign and be given a copy of the lease. This not only gives more leverage to the landlord but also binds the members of the group more closely together by emphasizing each member that he or she is held individually responsible for the fulfillment of all the provisions of the lease.

More and more landlords also are insisting that rent be paid by one check, hoping this will simplify payments and make the group work out any differences they may have themselves.

In addition, the mainstay of landlords and agents, the security deposit, also has been tailored to fit the group rental market. In some cases, groups are being required to put up two rather than the usual one month's rent as security deposit, and at least one real estate operator is reported to be requiring each member of a group to put up one month's rent as a security deposit. The legality of this latter procedure is open to question in some local jurisdictions.

One national trend the Washington area appears to be bucking, according to housing inspectors here, is the growth of the number of homeowners creating and renting apartments in their basements or upper floors.

The only local area where such "doubling up" is being done to any significant degree is Takoma Park, where even the few hundred holdovers from World War II gradually are being brought into compliance with housing regulations.

Nationally, the underground rental housing market in suburban and city single-family neighborhoods is booming. Owners are subdividing their home, often illegally, to meet rising utility, property tax and maintenance costs.

These rental apartments -- carved out of recreation rooms, the downstairs of split levels and upper floors of larger homes -- almost always are rented informally and without professional real estate help.

They also usually carry rents that are modest for their area. Typically they also violate local zoning ordinances, though some localities are beginning to allow "accesory" units in single-family neighborhoods.