The "Supersize Me" era of home building may be coming to an end after a three-decade run.

The size of the average new home swelled by about 50 percent from 1973 to 2006, but this trend toward expansion will probably be ending in the next decade, according to an elite panel of 135 builders, architects and designers surveyed by the National Association of Home Builders recently.

In a report released this month, these residential-construction experts said the downsizing tendencies of aging baby boomers, soaring home prices in much of the country and a fundamental change in consumer tastes will dampen future demand for ever-larger homes.

"People kept getting more and more and more space but felt dissatisfied because the space was not filling a void," said Sarah Susanka, co-author of "The Not So Big House."

"The moreness they were looking for had nothing to do with size" but rather with the craving for more intimate spaces they could use in more practical ways.

For decades, Americans have believed that bigger is better. The average size of a new single-family home in the first three months of 2006 was 2,459 square feet, up from 1,660 in 1973.

The size grew even as the average family size shrank, said Gopal Ahluwalia, staff vice president for research at the builders association. "So it's not as if people were buying bigger homes for functional use of space. It was about lifestyle. They were buying for the same reasons people buy expensive cars: because they could afford it."

But going forward, a new single-family home will most likely average 2,300 to 2,500 square feet in 2015, as it has since 2001, the survey found. Instead of focusing on space, homeowners will turn their attention to what makes that space special.

"People are not necessarily looking for square footage but for a home with a higher level of finish and detail," said Barry Glantz, an architect in St. Louis. "They want granite countertops, Sub-Zero refrigerators, Viking ranges, ceiling treatments, floor treatments. They want all the bells and whistles."

Glantz, who spoke about this topic at the International Builders' Show this month, calls these small but souped-up homes "jewel boxes." He noticed an unusually high number of them while judging the show's Best in American Living competition, in which the "Home of the Year" was a mere 1,200 square feet. These small homes, Glantz said, emerged as "one of the most significant trends" of the competition, which attracted 550 entries.

Richard Mandell, a Bethesda-based builder who specializes in in-fill homes, said he's seeing the same trend play out in the Washington region, where some of his clients have become more willing to trade house space for more yard space and many are asking for homes of a less imposing scale. It may be pressure from the neighbors, said Mandell, an owner of Sandy Spring Builders. "But I think it's really more about aesthetic preference."

Not everyone agrees that there is a trend or, if there is, that it's here to stay. Among them is Kira McCarron, chief marketing officer for Toll Brothers, one of the nation's largest home builders and a company with many projects in the Washington area.

McCarron said that during her 21-year tenure with the company, she's heard similar predictions about shrinking home sizes, particularly when consumers get spooked by rising energy costs. But these forecasts have not panned out in the past, she said.

"I don't believe the fundamental dream of bigger, better, more is going to end anytime soon," McCarron said. "I think people do like nesting spaces, but I think they like them in their 4,000-square-foot houses. They like the idea of reading areas, where they can curl up in the morning and read the newspaper. But they want one for him, for her, for the kids."

Some of the survey results appear to support that idea. For instance, while most of those polled said home size will not grow, 62 percent of them said that demand for two master bedroom suites will increase significantly by 2015.

Frederick Cooper, a senior vice president at Toll Brothers, said the bottom line is: "If you go to someone and say: 'Do you want more space or less space,' they would say more."

Cynthia Baker, a homeowner in Northwest Washington, lives the large-home/small-home debate in her own life.

Baker had more space in mind when her third child arrived. She and her husband, Jon Zeitler, decided to move out of their starter home and into one that's more than 3,000 square feet, with four floors, a big eat-in kitchen plus dining room, four bedrooms, two offices and an au pair basement suite.

But when her husband left his job in April, the family decided to travel through Europe and India, where they stayed in hotels and apartments, cramped into small rooms and living out of duffel bags. When the family returned home four months later, the house looked really big to them.

"It was sort of a revelatory moment," Baker said. "Life really does fill into the spaces we allow it."

They realized that they didn't need all that much space and that larger rooms draw more clutter. More time is spent cleaning extra rooms, such as the den, which Baker originally saw as the family gathering spot. But now that the television is in the basement, the den has become obsolete, she said.

Still, they probably won't move anytime soon.

"We can't necessarily afford a smaller house now," Baker said. "Isn't that the irony?"