ATLANTA — Greg Williamson had just finished a $12,000 renovation to his backyard patio, complete with a built-in barbecue, rock wall and flower garden, when a million-dollar monster was built next door.

Now, instead of enjoying a beautiful view as he basks in the sun, he stares across his driveway at a three-story brick house that is more than three times the size of his 1,400-square-foot bungalow. His neighbor's home is by far the largest on the block, but if the trend sweeping the country is an indication of things to come, it won't be long before someone comes along and builds a bigger one.

"Something like that changes the quality of life here," said Williamson, 44, a real estate agent who moved into his dream house in the affluent Morningside neighborhood in 1996 when a house similar to his sat next door. "I would rather have a trailer over there than that because it would be less intrusive."

Across the country, "McMansions" — sprawling houses on tiny parcels of land — are popping up in neighborhoods once known for their small, charming homes. As families, tired of long commutes from the suburbs, seek to move closer to their jobs in the city, they are tearing down those little houses and replacing them with 6,000-square-foot structures more typical of a suburban lifestyle.

It is a trend that has been going on for decades, but recently residents have begun to rebel and are enlisting their local lawmakers to place restrictions on McMansions or ban them. In Atlanta, one of the fastest-growing cities in the country, Mayor Shirley Franklin recently issued a temporary moratorium on the building of McMansions. But the City Council refused to extend it. Now the city plans to rewrite Atlanta's 24-year-old zoning codes to set new standards for how big is too big.

Other cities, including Dallas and Austin, Texas, also have tried moratoriums. Recently, Delray Beach, Fla., proposed halting construction of mini-mansions in five historic neighborhoods for six months. Evanston, Ill., issued a temporary ban in 2003 and last year instituted new building regulations: Houses could be no more than 40 feet high and cover no more than 35 percent of the lot.

The controversy has pitted neighbor against neighbor in a battle over aesthetics and property rights. Longtime residents say the big houses not only are eyesores but they also destroy the character of the neighborhood. Those who dwell in McMansions insist that as property owners, they have the right to build any size house they want as long as it meets city codes.

In some cities, the battle has gotten bitter. In Chevy Chase, Md., where a moratorium is in effect while officials figure out how to handle construction issues, Mayor Bill Hudnut had to urge residents to stop attacking each other.

"Egging someone's house, sending anonymous letters, some of them vicious ... expressions of hostility toward neighbors" should cease and desist, the mayor wrote in an open letter to residents.

Ultimately, experts said, the courts will likely decide the issue. In the meantime, city officials are struggling to strike a delicate balance, hoping to keep their longtime constituents happy while encouraging those who had forsaken the city to return and add to the tax base.

"It's been like a snowball once it got started," said Liz Coyle, a community activist who lives in the neighborhood bordering Morningside. "Before you can blink an eye, houses are gone, not just one but five."

Megahouses are a sign of the times, economists say. In typical keeping-up-with-the-Joneses fashion, everyone wants to outdo the neighbor.

"It seems to go in cycles. There have been periods of history where it was considered bad form to flaunt your wealth but we are not in one of those now," said Cornell economics professor Robert Frank.

The average size of homes in the U.S. has grown from 1,500 square feet in 1970 to 2,410 square feet today. At the same time, the average family size decreased from 3.11 to 2.57, said Gopal Ahluwalia, vice president for research at the National Association of Home Builders.