The best way to solve a wet-basement problem is to eliminate the source of the water, says a Falls Church housing consultant in a new do-it-yourself guide for homeowners.

While waterproofing contractors often attempt to correct wetness by sealing interior cracks and installing devices that remove the water already inside a home, those procedures deal with the symptoms rather than the cause, contends Michael P. Lennon, a former builder who lectures and advises on housing.

Since most wet basements in the Washington area--and throughout the United States--are caused by surface water that saturates the soil around building foundations, Lennon reports, creating a six-foot "dry zone" at the perimeter of a structure can be the cheapest, most-effective way to solve the problem.

"The Symptoms and Cures of Wet Basements," a 40-page manual written and published by Lennon, includes photographs and diagrams that illustrate how faulty construction and poor landscape design are often contributing elements. Lennon wisely asssumes that his readers are ignorant of basic construction practices, neatly explaining how cement parging inhibits leakage when troweled correctly onto foundation walls, for example, and why proper grading promotes a capillary action that draws moisture to the surface of the soil.

"It is virtually impossible to build a totally waterproof basement, but you can still have a dry basement by establishing and maintaining a dry zone around your house," Lennon advises. Among the do-it-yourself procedures he recommends:

Sealing exterior cracks in foundation walls and walkways with architectural caulking or a similar heavy-duty product.

Clearing rain gutters of debris and extending downspouts so they deliver water at least six feet from the house.

Transplanting foundation plantings at least six feet from the foundation.

Regrading soil at the foundation away from the house; tightly packing the soil and covering it with grass or mulch.

Although Lennon claims that saturated ground conditions account for 90 percent of all wet basements, he notes that other geological factors and construction weaknesses can cause wetness: Aquifiers--ground water trapped between soil and impermeable rock--may swell after heavy rains and seep through cracks in concrete floor slabs; frozen soil that is capable of holding more water than unfrozen soil can release excess mositure during rapid spring thaws; and springs created by seasonal rainfalls sometimes force water into basements.

In the infrequent circumstances when ground water--rather than surface water--is the causes the problem, often-expensive sump pumps may be the only solution, Lennon adds.

Lennon believes that while some waterproofing contractors are quick to remove dirt from around the foundation and repair the exterior of the wall, "this is very expensive, time-consuming and usually very unsuccessful." In addition, Lennon adds, "be extremely wary of any soil injection techniques since they have proven to be almost entirely ineffective."

While standing water is the obvious sign of a wet basement, prospective buyers can determine hidden wetness problems by looking for subtler symptoms, Lennon suggests. In unfinished basements, peeling paint, interior parging and floor stains are indicative of wetness. In finished areas, telltale indicators include rusty nailheads, warped paneling and discolored tile glue. Outside a house, moss growing near foundation walls, downspout erosion and patios that slope toward the structure may mean that the basement is wet.

Lennon points out that a damp basement--caused by condensation of warm, moist air--is not at all the same as a wet basement. If a piece of foil taped to a basement wall develops moisture on the front (but not on the back), dampness is the problem and a dehumidifier is the solution.

A recent Fairfax County report on basements in new housing concluded that poor construction and a lack of minimum standards are the primary causes of wetness. Researchers said that dense clay soil prevalent in the region call for special attention paid to parging and grading in order to insure a dry basement. In addition, the report blamed poorly installed downspouts that deposit rain water too close to foundations and inadequate concrete flooring that frequently cracks.

A study of wet basements conducted last spring by Washington Consumer's Checkbook found that an inexpensive, do-it-yourself solution worked on one test house in which the basement flooded after rainstorms. The group spent about $300 dollars sealing cracks in the foundation and regrading the surrounding soil. Heavy rain feel soon after the project was completed, but Checkbook researchers found no leaks.

Despite that success, the group pointed out that each wet basement is unique and homeowners can not count on the same result. The group added that waterproofing contractors often propose extensive treatments to make sure that all leaks are sealed--thus avoiding repeat visits for warranty work.

"The Symptoms and Cures of Wet Basements," is available for $5 plus $1 postage from Homepro Systems, Inc., 110 W. Great Falls St., Falls Church, Va. 22046. Phone orders may be placed by calling (703) 241-3815.