In the highly competitive Washington-area housing market, builders know that an attractive model home often proves the difference between selling a house and having the would-be buyer walk out the door.

But buyers often find that the new home they bought after admiring the model may not turn out exactly the way they wanted.

Buyers and developers agreed that models always are designed to show a condominium, town house or home at its best. That often means the model includes many optional items that would make the house unaffordable to those who are attracted to the development by the advertised price range.

Industry sources said buyers like to see what they are thinking of buying at its best, even if they cannot afford to buy everything to make it the house of their dreams.

"You are seeing the whole dream and buying the potential," explained Bob Coursey, marketing services manager for the Maryland region of Ryan Homes, one of the largest developers in the Washington area.

Nonetheless, several couples interviewed in recent days said they "fell in love with the model" before they bought and then realized what they were getting would not include everything they had seen.

One couple looking at a development near Reston complained about the $4,500 cost of adding a wrap-around porch to the three-bedroom home they have decided to buy. The model they saw included the porch, and the couple, who asked not to be identified, said they assumed it came with the house.

But the couple said it was not until they had eliminated dozens of other possible homes that they realized they still wanted to buy the original model and pay the extra money for the porch.

Some prospective buyers said that furniture smaller than what most people own often is displayed in models to exaggerate the sizes of the rooms. Several said dining rooms with half-walls overlooking living rooms look good and give buyers a feeling of spaciousness, but fail to provide wall space for a china cabinet or buffet.

Another couple said they admired a Centreville model's shrimp-colored walls that were accented by combinations of expensive wall coverings and picture-perfect art, but only later discovered they could not afford such options. They also could not afford the optional built-in bookcases in the living room, guest bedrooms and family room. So were the hardwood floors and skylights that enhanced the models.

"I am smart enough to know that the large mirrored walls are there to make me think this room is bigger than it really is," said one man looking at a home in the $135,000 price range near Washington Dulles International Airport. But he said this has not hindered his continued interest in the development.

Lori Poirier, who is setting up a consumer-oriented organization in Falls Church known as Consumer Housing Library, said she believes models "are not good" for sellers or buyers because they do not set up the best working relationships for either party.

"The consumer may walk into a model with a hostile attitude" because he does not want to deal with sales pitches, she said. A model "puts a false cover on the actual product," Poirier said.

She also cited a recent case where a buyer paid $3,000 extra for a "premium" lot backing up to heavy woods at a Falls Church development, only to discover after moving in that the woods would be knocked down to make way for the second section of the project.

Some builders agreed with prospective buyers who were interviewed that models can be deceiving.

"Decorators are hired to maximize the potential of the unit, but not to be deceptive," said Dwight Schar, head of NVHomes, a major home builder in Maryland and Washington.

Several builders said they make special efforts to ensure that would-be buyers know exactly what they are getting in the basic home model they are buying and what options cost extra. Schar said his company provides checklists that sales personnel are supposed to review with prospective buyers so they know what is standard and what is optional.

Despite the disappointments that some buyers say they encounter, others said they still prefer looking at models rather than at the brochures, maps, glossy color photographs and site plans that some builders use when they sell homes without building model homes for prospective buyers to view.

Some projects are selling out before the foundation for the first home is poured. These homes often are in prime locations and are being built by developers with good reputations for constructing a quality product for a reasonable price, industry sources said.

The shortage of available housing and the rush by consumers to buy while interest rates are relatively stable has led some builders to use models in one development for models in another nearby project.

A large sign saying "Only two left" covers the name of a Tipco development on Braddock Road near Route 123 in Fairfax County. There isn't a house in sight, only a sales trailer near the road in front of a red mud field that soon will be filled with so-called move-up homes in the $200,000 price range. Sales agents at the site pass out brochures about the development and maps to models at another nearby Tipco development, Camelot Green.

Tina Aquillino, marketing director for Long & Foster's new-homes division, which represents Tipco, said the fact that there are only two homes left out of the planned two dozen in the Braddock development is in keeping with recent trends that company has experienced.

"At a development known as Wide Awake in the Sleepy Hollow area of Falls Church, Tipco sold $3 million worth of homes in September out of a sales trailer," she said. "We do have the advantage of sending people to models" at other projects.

When operating out of a trailer, "It is critical to have portfolios, glossy photographs and detailed maps" for buyers to see, Aquillino said.

If the home under construction is different from anything being built nearby, a model is extremely crucial, industry sources said.

E. Roger Oien of Century 21, Kidder Associates Inc., who is handling sales of passive-solar contemporary homes in the Suncatchers' development in the Countryside community of Loudoun County, said, "In this price range more than $160,000 , a model is essential." Buyers "want to know what they are getting for their money. They have to see it."

Other builders agreed that move-up buyers demand models. "You can't get emotional over a brochure," Ryan official Coursey said.

Even though most developers said the Washington buying market is educated and sophisticated in every price range, developers said many people still shop with their heads but buy with their hearts.

Coursey and Gary Garczynski, head of Signature Communities and president of the Northern Virginia Builders Association, cautioned that models must be designed to fit the market. Both said putting up expensive wall and window coverings and elaborate furnishings in a town house aimed at a first-time buyer can be a major mistake.

"We still plan for models on all Signature sites, but don't always follow through because the development may sell out before the model is finished in this market," Garczynski said.

Signature always displays "a 'buyers' beware' sign that tells exactly what goes with the unit and what does not," Garczynski said. "You have to be careful not to merchandise the unit out of the ballpark" for the buyer, he said.

Garczynski said sales from trailers based on brochures, drawings and maps are more likely to be risky for consumers than sales from model homes.

"There is more of a chance in the pre-sale when a buyer makes his purchase before the first unit is started," he said. "They have to be as careful as possible."

Still, industry sources cited advantages to buying from trailer sites before builders have invested in the cost of constructing a model. The cost of building and furnishing models is passed on to buyers, and purchasers often can get the best prices and sometimes the best locations if they are willing to take a chance on buying before ground is even broken, developers said.

Jane Anderson, director of sales and marketing for The Anden Group, said her company has sold from trailers for years. But that policy will be changing. "We will try to put up at least two models in our developments in the future," she said.

Anderson said sales made without models are almost "always subject to viewing" of a finished unit by a buyer, a practice that sometimes can force a company to sell the unit twice -- once from promotional materials and once after a model is built.