Washington area new home buyers are paying an increasing percentage of the cost of the property for the land underneath a house, a trend that is mirrored in other high-priced communities in America.

Conversely, local homeowners can blame rising property tax bills mostly on the growing value of the land relative to the bricks and sticks in their house.

Such are the dynamics at work as a run-up in Washington area land prices has claimed a larger bite of the total price tag paid for a home.

Conventional wisdom holds that 25 percent of a new home's price tag goes toward the cost of the land. But soaring lot prices here have left that rule in the dust, according to local builders and developers.

Home buyers now are spending closer to 30 percent of the ultimate new house price on land, builders said. They said the relative cost can run as high as 40 percent in some close-in, high-demand neighborhoods.

In fact, a buyer has to go as far out as Mount Airy in Frederick County, 30 miles north of the District, before land costs add up to only a quarter of the price, said Robert Mitchell, president of the construction firm C-I/Mitchell & Best.

Washington's experience is not unusual for a high-cost market. A new survey of residential lot prices conducted every five years by the Urban Land Institute points to similar trends.

The 30-market study, which did not include Washington, found that the price for an improved quarter-acre lot rose much more quickly than the general inflation rate in some of the country's hottest real estate markets.

San Jose, San Diego and Seattle all weighed in with annual lot price increases of 20 percent or more for each of the past five years. Builders in Boston saw prices go up nearly 15 percent annually in the period.

Although data on lot prices in the Washington area are spotty, builders say that the local situation mirrors those of the other high-priced real estate markets.

"Twenty percent a year for the past five years is not very far out of line" with what has happened here, said Frederick A. Kober, president of the Christopher Cos., a Northern Virginia and Montgomery County builder.

What's more, land looks like a bargain here compared with how much of the price tag it accounts for in some other cities. In San Diego, a quarter-acre lot typically costs $150,000, according to the survey, and thus would account for a whopping 72 percent of the median price paid for new and existing homes in the first quarter of the year. In Seattle, the typical $77,500 lot represents 57 percent of the final house price.

However, the lot-house relationship suggested by the land institute study may not be truly representative, warned Tom Black, the trade group's vice president of research. A quarter-acre lot in many communities now is much more rare, and therefore relatively more expensive, than it was when the study began in 1975, he said. So, an atypically large lot size would skew the lot-house relationship too heavily to the land side.

In the Washington area, the majority of quarter-acre lots are found outside the Capital Beltway and are not cheap. Lots of that size, Kober said, cost at least $100,000.

Anthony Natelli, a partner in Potomac Investment Associates, the developer of the Avenel golf course and residential development, agreed with Kober's assessment.

But he stressed that location plays a significant role in what a builder pays for raw land. A quarter-acre lot in Germantown, he said, would sell for $90,000, but at Avenel, just outside the Beltway in Potomac, the going price is $300,000.

The impact of land-driven price increases goes well beyond the new home market, said Susan Matlick, executive vice president of the Suburban Maryland Building Industry Association. The effect also is felt on the resale side of the market, she said. The reverberations also catch up with homeowners when property tax bills start to reflect the change on existing home sale prices.

The softening in Washington area real estate prices over the past 18 months has, however, reined in galloping lot prices, several builders and developers agreed.

But there are differing opinions on whether land prices are appreciating more slowly than in recent years or actual price reductions are occurring.

Kirk Kubista, vice president of land for Ryan Homes, said he believes that both points of view are true. He said he has witnessed a slowdown in the appreciation rate on some land. But in other cases, he said some land speculators who paid too much for property during the housing boom years that ended around 1988 are now having to offer prices discounted from what they paid in order to sell the parcels.

In some cases, the market downturn has effectively pushed the price ratio of land to house still higher, said Roger Snyder, chief executive of the Northern Virginia Building Industry Association. Some builders, he said, are now erecting less expensive homes on lots purchased six to nine months ago with more expensive housing in mind.

When the real estate market does rebound, land costs are poised to take off again because of a shortage of lots, members of the building community warned. A year from now, land prices will prove "troubling for all of us," Kober predicted.

The local building industry has already cut back on land development, said Gary Garczynski, chairman of Long Signature Homes. "Until the down cycle runs its course, whether that is in 1991 or 1992, not a lot of lots are being manufactured."

Mitchell said there is a growing reluctance among lenders to finance land acquisition and development, which may be a precursor of a new run-up in lot prices. Builders cannot build on as many lots at one time, he said, because they have to invest more of their own cash in purchasing fewer lots before construction ever begins.

Environmental constraints, from wetlands preservation to storm water management to tree preservation, also force builders to put up fewer houses than planned on a parcel of land, builders claimed. That in turn drives up the relative cost land plays in the final house price, they added.