The movement has rapidly been gaining traction: Its proponents are ascending to prominent positions at architecture schools, its practitioners have won significant commissions around the world, and respected publications like ArchitectureBoston and the European journal Topos have recently devoted nearly entire issues to their ideas. MIT has launched a program called Landscape+Urbanism; Northeastern University will soon offer an undergraduate degree in urban landscape. “This whole thing is hot stuff at the moment,” said Phyllis Andersen, a landscape historian at the Landscape Institute of the Boston Architectural College.

At the heart of the landscape urbanist agenda is the notion that the most important part of city planning is not the arrangement of buildings, but the natural landscape upon which those buildings stand. Proponents envision weaving nature and city together into a new hybrid that functions like a living ecosystem. And instead of pushing people closer together in service of achieving density, as New Urbanism advocates, landscape urbanism allows for the possibility of an environmentally friendly future that includes spacious suburbs, and doesn’t demand that Americans stop driving their convenient cars. Americans have decided how they want to live, they argue, and the job of urban designers is to intelligently accommodate them while finding ways to protect the environment.

“We criticized it and called out all the contradictions, and we laughed and we made fun of him,” Duany recalled by phone recently. “And then when we were done, I said, ‘OK, but is there one kid in that room who isn’t leaving a convert?’ ”

At one point during the huddle in New Orleans, Duany projected a video onto the dining room wall of a lecture delivered by Charles Waldheim, the intensely confident, spiky-haired leader of the landscape urbanism movement. Waldheim, 47 years old, had recently been appointed chair of Harvard’s landscape architecture department and was now filling it with his allies. The video, in which Waldheim, dressed in all black, spoke to students at the University of North Carolina, played for just over an hour.

The purpose of the summit was to talk about an enemy. A rival faction of urban theorists had begun to publicly challenge them, and declare their approach to city-making obsolete. Calling themselves landscape urbanists, these upstarts were promoting themselves as environmentally conscious, ecologically sophisticated, and uniquely suited to bring sustainability to America’s suburbs. Instead of talking about buildings, street grids, and parks, they spoke seductively about “living processes,” “flows,” and the importance of respecting “ecological infrastructure.” Their ideas were being embraced in the architecture world as radical and new. Most disconcertingly, they were rising to power at one of the most influential architecture academies in the country: the Graduate School of Design at Harvard University.

A little over two months ago, some two dozen influential architects, urban planners, and academics from around the country gathered at a New Orleans cottage to spend a long weekend discussing strategy. The house belonged to 61-year-old Andres Duany, a leader in the movement known as New Urbanism, which originated in the late 1970s and has enjoyed decades as the dominant force in American city planning, urging Americans to reject suburban subdivisions in favor of denser, more diverse neighborhoods.

The first New Urbanist development broke ground in 1981 in Seaside, Fla.; behind the controls was an architecture firm founded by Duany and his wife, Elizabeth Plater-Zyberk. In sharp contrast to a typical new development, Seaside took shape as a compact grid of narrow, tree-lined streets laid out around a walkable downtown with stores and civic spaces. The town was featured on the cover of The Atlantic Monthly and in Time magazine, and the movement grew in popularity. Today the Congress for the New Urbanism boasts a membership of more than 3,000, and its principles have guided the planning of hundreds of American communities. In recent years, proponents of the New Urbanism have also begun claiming the “green” mantle, arguing that denser settlement is not just better socially, but also more efficient: Walkable spaces mean less time in the car.

Yet a growing number of architects and urban planners regarded the transformation with dread. They watched as cities were hollowed out, replaced by soulless subdivisions, strip malls, and office parks, and they began to formulate an alternative. The “New Urbanism” offered a vision of denser, more diverse towns where people could walk to work and to the store — places where neighbors might wave hello to one another from their porches instead of climbing into car in a detached garage and driving away alone. The nightmare of suburbia, they believed, was one from which America could still wake up.

How should Americans live? The roots of the current debate lie in this country’s transformation after World War II, when millions of middle class Americans started leaving their homes in the city for cheap and spacious new houses on the outskirts of town. They bought cars en masse, and thanks in part to the Federal Highway Act of 1956 , they could use them to get almost anywhere. By the end of the 1950s, a front lawn, a backyard, and a car in the driveway had become symbols of autonomy and prosperity. The nation was reconfiguring itself into a patchwork of low-density settlements that became known as suburban sprawl.

Both the landscape urbanists and the traditionalists they’re trying to unseat think they know what must be done to conserve energy, limit emissions, and protect the environment from further harm, and both are certain that the other is wrong. As they joust in the pages of architecture publications and take swipes at each other from podiums, they are competing not just for commissions, but for the hearts and minds of a generation of young planning students who will soon be moving into positions of real influence themselves. At stake is the future of cities and their surroundings — what they will look like, how they will work, and what it will be like to live in them.

But to skeptics, Waldheim and his cohort are merely riding to fame and fortune on a skillfully promoted brand name, environmentalist rhetoric, and a lot of obscure theory. Critics have charged landscape urbanism with advocating a misguided surrender to suburban sprawl — a “green” agenda that dooms America to a future of dependence on highways and automobiles. And they are cloaking it in language so abstract that it has inspired a mocking website: a landscape urbanism jargon generator that randomly spits out phrases like “enhance permeable operations,” “allocate temporal contexts,” and “orchestrate sustainable metrics.”

Taken together, those two positions add up to a vision of city planning that doesn’t put a priority on city life over suburban living; it focuses instead on resource protection, the creative use of natural infrastructure, and so-called systems thinking — that is, exactly what landscape architects are trained to do. There are, as yet, few examples of the ideas put into practice: Supporters tend to point to projects still under construction, like the park being built on top of a landfill in Staten Island, N.Y. But Waldheim has said that his program is “specifically” and “explicitly” meant to dislodge the New Urbanists from their perch in the American planning world.

The landscape urbanist vision propounded by Waldheim and his allies comes down to two central insights. The first is that American cities in the 21st century are not like American cities from the 19th century, and should not be expected to function the same way. The second is that the best way for urban designers to protect the environment is to prioritize the natural landscape. Design should accommodate the waterways and the wildlife that were there before you arrived; it should preserve the rainfall instead of shunting it into sewers, and perhaps use it to irrigate nearby vegetation.

Among those training at Penn during the late 1980s was Charles Waldheim. In 1997, as an assistant professor of architecture at the University of Illinois, Waldheim organized a conference that would function as an “intellectual rollout” for what he believed was an entirely new way of looking at cities. He coined a term for it, “landscape urbanism,” and within a few years, it began to catch on in academia. The “Landscape Urbanism Reader,” edited by Waldheim, was published in 2006, and in 2009 he was hired to chair Harvard’s landscape architecture department and told to oversee the appointment of 10 new faculty members — effectively a mandate to transform Harvard’s Graduate School of Design into the movement’s new intellectual nerve center. (Though the landscape department is just one of three at the school, support for landscape urbanism runs all the way to the top: The school’s dean, Mohsen Mostafavi, is considered one of its leaders.)

As the New Urbanism was growing in influence, another movement concerned with city-making was quietly beginning in an unlikely corner of the academy: landscape architecture. The field had spent most of the 20th century being seen as something of a backwater, an ornamental craft whose practitioners were responsible for making things pretty once the work of designing buildings was complete. But landscape architects had expertise in something that most planners and urban designers were not trained to think about: ecology. Starting at the University of Pennsylvania in the ’80s, landscape architects started to argue that their training meant they shouldn’t just be consigned to “putting parsley on the pig,” in the words of Australian landscape urbanist Richard Weller.

“It’s a critique of the models we’ve had available in urban design and urban planning for the last decade or two,” Waldheim said a few weeks ago, in an interview at the Isabella Stewart Gardner Museum, where he was recently made consulting curator of landscape architecture. “But really, more than a critique, it’s a kind of alternative.”

In their lectures and writings, Waldheim and other landscape urbanists paint the New Urbanists as nostalgically stuck in a conception of city life that ignores the changes brought by the modern service economy, the Internet, and the highway system. Americans have unequivocally demonstrated that they would prefer to live spread out, and the landscape urbanists argue it’s a delusion to believe that one can force the toothpaste back in the tube with zoning laws and design schemes.

“This notion of city center and suburb is a counterproductive differentiation,” said Pierre Bélanger, one of the new landscape professors at Harvard. “Cities and suburbs are actually part of urban economies.”

Proponents of the New Urbanism have not been taking the accusations of obsolescence sitting down. In a widely circulated November essay on the website of Metropolis magazine, Duany mockingly cast the rise of landscape urbanism at Harvard as a “classic Latin American-style...coup.” His fellow New Urbanists have weighed in with more substantive critiques that have been equally harsh. One planning professor in Arizona attacked the landscape urbanists for caring more about nature than humans; on the planning website Planetizen, the Portland, Ore.-based urban design theorist Michael Mehaffy published an indictment of landscape urbanism called “Sprawl in a Pretty Green Dress?”

The underlying argument between the groups goes beyond the relative merits of density, or the question of whether you should start a planning project with the buildings or with the watershed. It’s an argument about whether human beings should adapt to the conditions in which they find themselves, or try to change them. Is sprawl inevitable, or isn’t it? At what point does it make sense to come to terms with it and try to find pragmatic, incremental solutions that don’t rely on any paradigmatic cultural shift?

The New Urbanists have always argued that sprawl is the result of specific policies and habits. Their belief that those can be reversed motivates their entire agenda. “The idea that there is nothing we can do because the market simply dictates sprawl, well, that’s just not true, because there are rules and regulations that are creating sprawl and undergirding it,” said Emily Talen, the Arizona New Urbanist. “That means it is possible to change those things and redirect urbanism in a different way.”

But landscape urbanists don’t think that we should be trying to change those things — that doing so would be close-minded and futile.

“The overwhelming majority of discourse in urban planning and design has been biased, has been kind of prejudiced to the idea that Manhattan-ism is the most sustainable urban future,” said Waldheim. “On the one hand, we know that density addresses a number of issues, but on the other hand, as soon as you say, ‘Where does your milk come from?’ we have a whole different set of questions about sustainability.”

For Waldheim and the landscape urbanists, what comes next is translating their ideas into real, built projects. As they do, they’ll be forced to contend with the normal difficulty of ushering theories into the world beyond the university gates. But there’s also something else waiting for them: Duany and his compatriots, bringing a schoolyard-style enthusiasm to the rivalry.

“What you’re seeing is the New Urbanism about to swallow the landscape urbanists,” Duany said. His plan now, he said, is to systematically “assimilate” the language and strategies that have made his opponents such a white-hot brand. “We’re trying to upgrade ourselves. I’m not gonna say, ‘We’re gonna flick ’em off the table because they’re a bunch of lawn apologists.’ I’m gonna say, ‘For God’s sake, these guys took over Harvard!’ ”

Leon Neyfakh is the staff writer for Ideas. e-mail lneyfakh@globe.com.

© Copyright 2011 Globe Newspaper Company.