ON A RECENT inspection of a new house in Woodbridge, Va., professional home inspector John J. Heyn found nearly 100 defects. The inadequacies included missing steps, insulation fallen off under the floors, holes in the masonry block foundation walls, floor joists without the necessary metal hangers, leaking dishwasher, closet shelves without bracing, drains blocked with concrete, water faucets not operating, loose downspouts, grading that was too high in the front yard and wood stumps and vines growing in the crawl space.

Houses such as this one are providing rich fodder for a thriving home inspection business in the Washington area.

About seven years ago, Claxton Walker received a call from the phone company. Walker, who has an office in Potomac, inspects houses for people buying, remodeling or selling them. The phone company said he was one of two professional home inspectors. Did he know of a third so they could make a special listing in the Yellow Pages? Today the listing, under "Building Inspectors" contains more than 20 names.

One of the reasons the home buyer uses our service is to find out what are the present problems and what are the potential problems" in the home he plans to buy, said Heyn, president of the American Society of Home Inspectors and owner of a firm that operates in the Washington-Baltimore area.

You can usually expect an older house to present problems you will have to fix after you buy it and you plan for these by putting money aside. If you don't see them coming and don't plan for them, then you are either unlucky or foolish or maybe just not thinking and you get stuck. Now many people who are buying new homes - homes that have just been built - say they are being stiffed.

"Our percentage of new homes is growing each month," Heyn said. "Probably 25 percent of our business is with new homes prior to presettlement walk-through. People are getting short-changed on some of their new houses. Mainly not through willful neglect or cost-cutting, but through lack of supervision and lack of pride in workmanship."

Inspectors say that at today's prices, home buyers are increasingly fearful of additional - and unforeseen - repair costs.

"It's the fear of the unknown that kills the deal," Walker said.

Some experienced buyers prefer component specialists (electricians, plumbers, heating engineers) to whole-house generalists. And prices can vary, but usually run about $100, more or less, for a complete inspection. Some inspectors charge a flat fee and others base their price on the value of the house. For about $150 Walker will spend two hours with you walking around the house and telling you what's wrong with it. His written report describes the condition of the house: from the landscaping, to the chimney; from the basement to the roof; from the furnace to the attic fan; from the insulation to the plumbing.

Walker tells you wnat's wrong with them, when you can expect them to break down and approximately how much you should set aside to put them back in good repair.

There is no affection lost between professional home inspectors and many real-estate agents. "To be in sales," says Walker "you've got to be optimistic." Walker's reports are not always upbeat. "I don't give a damn if the sale is made or not."

Snags are the last things real estate firms want in their sales and the inspector's report become a bargaining tool in the hands of the buyer. "The buyers can say, "Look, I'm still interested in the house, but I'm not going to pay top dollar because I'm going to have some problems here." The majority of people buy the house we inspect. So we don't kill sales. They negotiate the price to compensate for problems we find," Heyn said.

Some real estate firms have apparently countered by offering their own "pre-sale inspection" or warranties covering major components. (The National Association of Home Builders encourages members to participate in the Home Owners Warranty Corp., which offers a limited warranty and 10-year insurance program to cover faulty construction.) Some agents are coming around to the idea of independent inspectors, however, as a hedge against trouble with buyers, after the sale is made.

"It puts my mind at ease," said Fairfax broker Palmer Robeson, who is also on the home protection committee of the Northern Virginia Board of Realtors. "Some new home buyers blow things all out of propotion. They won't believe me when I tell them it's all right, but when they pay an inspector $100, they will believe him. I don't like to call the people later and ask "How's it going?" and they say "The air conditioner is broken, the roof is falling in - you sold us a lemon." How do you think I feel then?"

Claxton Walker rarely has time to complete a sentence because he talks too fast. He waves his big hands and jumps from one idea to another like a mountain goat. But if you think he must be the man who taught you how to wrestle in high school you will be wrong. He coached football.

Walker taught industrial arts at a private high school in the Washington area. The ex-Marine who was stationed in the Pacific during World War II left teaching for home repair and remodeling. "I put an ad in the paper and my first job was fixing somebody's window. I learned a lot about the so-called better builders when I started tearing their homes apart."

After a few years of building new homes, he tried teaching again. "I was too old. I couldn't hack it." So he turned to inspecting houses.

Inspectors find that wet basements are the most common complaint.After a time, they learn that "certain neighborhoods always have water problems," said Walker. "You can make water go where you want it to go. And when you don't, that's when you have problems." Walker first inspects the grading around the house and the downspouts and gutters. He looks for long splash stones under the downspouts and if they are not there he recommends installing some. If the slope from the house is insufficient, he will estimate the cost of putting in more soil.

He knows the normal lifespan of major appliances and can tell you when the galvanized steel plumbing will likely need replacing. He knows how long a slate roof is supposed to last so when the roofer says it needs to be replaced, Walker tells the client to make sure the roofer is there when he inspects it. "Most of the time," Walker says, "the guy won't show up."

Walker is one of the early members of the American Home Inspectors Society, a group that has grown to about 200 in the last three years. Full membership requires logging 1,000 inspections.

"We do not do any home repair or remodeling work and we do not recommend anybody," said Heyn. "So if a home inspector says you have a bad roof or a leaky basement and in the same breath tells you he has a friend who can fix it for you, I'd beware."

Some inspectors carry "error and omission" insurance, a type of malpractice coverage that guarantees the inspector will be able to pay for mistakes. Most experienced home buyers will insist on a caluse in their sales contract making the sale contingent on a satisfactory survey of the house by a professional home inspector, or by a favorite builder, architect or engineer. The clause allows a certain number of days for the inspection and for the buyer to decide if he is satisfied before the sale papers must be signed.

Not all sellers will accept such contingency clauses in their sales contracts, however. You must decide whether the risk of losing the house to another buyer who is more trusting outweighs the possibility of unpleasant surprises.

Most inspectors prefer the buyer be on hand during the inspection and that the inspection be made during the pre-settlement walk-through with the seller or builder.

"I've seen as many as 60 deficiencies," said one inspector. "There are some cases where the builder's representative is a salesperson and he doesn't know anything.Some of these guys will say, "Okay, just walk through the house and tell me what's wrong.""

Many home buyers move in and discover they have problems because some work was never done. The basement leaks because the grading wasn't completed; the house looks awful because the gutters were never painted.

"Builders are moving people in before the houses are finished," said Walker. "All they want is the money because they need it to start on another project. Once they've got it, they have no incentive to come back." CAPTION: Illustration, no caption