Last week President Bush -- who has made his 1,600-acre Texas ranch and its seemingly boundless horizons a symbol of his presidency -- asked the nation to recognize some limits.

Trading in his rugged individualism for a summons to collective restraint, this former oilman and avatar of the nation's long-standing faith in endless abundance asked Americans to join car pools and run appliances at off-peak hours. "We can all pitch in by using -- by being better conservers of energy," Bush said in response to a reporter's question, pledging to make the federal government a role model in this regard.

The president's call for conservation -- as mild as it was -- marks something of a turnaround for the Bush administration. In April 2001, Vice President Cheney famously dismissed energy conservation. It "may be a sign of personal virtue," he conceded, but could hardly supply the foundation for "a sound, comprehensive energy policy." A few days later, Bush said conservation could play a role, but reaffirmed his vice president's position: "We can't conserve our way to energy independence, nor can we conserve our way to having enough energy available."

Bush's appeal for national sacrifice represents more than a tweaking of energy policy; it reflects a broader shift in the president's -- and the nation's -- sense of what's possible, and what isn't. For all of his efforts to convey the can-do spirit, Bush reluctantly finds himself echoing the much-maligned pronouncements of the Carter era. He's stuck in a new age of limits.

This is not the image that Bush tried to project for the past five years. Only a month ago, before the twin hurricanes pushed gasoline prices over the $3 a gallon mark, he was enjoying his sprawling Crawford homestead, whose self-conscious evocation of the nation's frontier heritage has vividly encapsulated Bush's confidence in America's capacity to remake the world and his vision of the individual entrepreneur as a modern-day pioneer. But the White House seems a more apt setting for him now: a place where he's boxed in by the dreary news from Iraq, the bickering among his own party's members of Congress, the roller-coaster oil markets, and budget deficits that make any talk of new initiatives obsolete.

While President Bush has not embraced the idea of limits the way President Jimmy Carter once did, he's been forced to accept them nonetheless. Bush isn't going to make televised speeches wearing a cardigan sweater like Carter; he's well aware of how that speech hurt Carter by diminishing him and making him seem less presidential. But by embracing conservation measures he had earlier belittled, Bush acknowledges at least temporary constraints on energy consumption. By talking in recent months of pulling even some U.S. troops out of a chaotic Iraq, the White House is implicitly recognizing American military power's inability to remold the world and his inability to rally domestic public opinion. And by quietly abandoning his quest for Social Security reform, Bush has conceded his circumscribed sway over Capitol Hill.

Most important, the president's post-Katrina appeal to civic virtue recognizes limits on the ability of the unfettered marketplace to solve the nation's pressing problems. For five years, the administration relied heavily on market mechanisms -- stressing entrepreneurship and individual initiative as the best approach to a wide range of policy questions. Even after the Sept. 11 attacks four years ago, the president refused to call the nation to patriotic sacrifice, instead urging the country to shop its way to recovery.

The embrace of gasoline conservation extends a broader administration emphasis on civic virtue and collective action over the past year. Recently, he has made broad commitments to rebuild the Gulf Coast and uplift the region's long-suffering impoverished population. Bush's recent rhetoric, with its appeals to community and shared national destiny, recalls the Carter administration's promise "to restore and re-create our sense of community and of the common good."

Traditionally, Americans don't like limits. From the beginnings of the nation's history as a distant New World outpost, Americans have remained a people of plenty, convinced (sometimes against overwhelming contrary evidence) of the nation's boundless abundance and limitless opportunity for citizens to reinvent themselves. Endless highways, not dead-end streets, define the national imagination.

But 30 years ago Americans found themselves grappling with the apparent arrival of an age of limits -- on presidential power, U.S. military power and U.S. economic power. Richard Nixon believed that America had exhausted its glory days as the unquestioned world leader and that it faced a more challenging international environment. Gerald Ford concluded that inflation and stagnation would force Americans to curb their insatiable appetite for ever more goods and services. Carter famously declared that "We have learned that more is not necessarily better, that even our great nation has its recognized limits."

During the winter of 1976-77, oil and gas shortages shut down assembly lines and closed schools across the country. Like today, nature also seemed to be conspiring against us: Snow actually fell on Miami Beach and solid ice stopped barges on the Mississippi. In Detroit, the once-proud symbol of American industrial might, the utilities reduced voltage, dimming lights and darkening moods across the state of Michigan. "The great American ride," as novelist John Updike called it, 30 years of unchallenged power, uninterrupted progress and unbroken postwar prosperity, had run out of gas. Calls for discipline and sacrifice filled the airwaves.

But Americans still did not want to accept Carter's vision of limits. The programs he put forth to address those limits withered. Amid the mayhem and malaise of the '70s Americans looked elsewhere to solve their problems and define their communities.

That led to a fundamental political and cultural shift that fueled Ronald Reagan's victory in 1980. Insisting on abundance, the nation and its leaders rejected calls for conservation or regulation. Instead of accepting limits, Americans blamed government for failing to remove limits. The nation and its leaders, even later within the Democratic Clinton administration, looked more to Wall Street than to Pennsylvania Avenue. The Texas oilmen who now occupy the nation's two highest offices embodied that anti-government, entrepreneurial ethos.

The dismal, malaise-filled '70s offer some cautionary lessons for today's shifting political landscape.

Like Bush's Republicans, Carter's Democrats enjoyed strong majorities on Capitol Hill. But Carter could not discipline his party faithful. He never could persuade them to accept what he saw as necessary adjustments to a changed political landscape. Congressional Democrats rejected his call for a balanced budget, a wage freeze for government employees, and an end to federal controls on natural gas prices. He was "continually torn," according to his top economic adviser, "between his own basically correct, substantive instincts and the need to satisfy the coalition that elected him."

In the wake of Hurricane Katrina and in the face of continuing difficulties in Iraq, Bush also finds himself on the cusp of a new political order. He is pointing the nation -- and his party -- in directions different from those in his first term. Abroad, he has been more multilateral, and at home he has stressed a more communitarian sense of collective responsibility, in contrast to his earlier encouragement of Americans to help their country simply by exercising their individual self-interest and opening up their wallets. The centerpiece of this new governing philosophy, of course, is the massive and hugely expensive recovery program for the Gulf Coast.

But like Carter, Bush faces potential mutiny from his own base in Congress and the electorate. Aware of that danger, he has tried to sell his new wine in old bottles, simultaneously stressing the responsibilities of the federal government and the need to promote entrepreneurship, advocating energy conservation but refusing to put on the table sterner measures like those implemented in the Carter years, such as a "gas guzzler tax" on low mileage cars or new fuel efficiency standards for buildings, cars and refrigerators.

Much has changed since the late 1970s, and Bush might be better equipped to navigate the shifting political currents than Carter. Still, it remains difficult for any sitting president to negotiate so complex a maneuver in midstream. One illustration may be Bush's effort in 2004 to invoke the spirit of the New Frontier by endorsing a manned space mission to Mars. "We choose to explore space," he asserted, "because doing so improves our lives and lifts our national spirit." Yet instead of rallying the nation, Bush seemed to succeed mostly in sparking discussion of the scientific and budgetary limits that made such a mission seem so difficult -- and thus unlikely.

In much the way that the end of the Carter years and the advent of the Reagan Revolution marked a paradigm shift in American public life, the Bush administration might be experiencing another such political realignment. And like Carter, who could not clearly perceive how to escape the constraints of the expiring old order, Bush's grudging, incomplete acknowledgement of the need for conservation reflects a reluctance to fully accept the new era of limits. And that might hinder his ability to deal with it.

During that past age of limits, Carter presided over a transitional presidency, one in which the old liberal politics no longer worked and no one had yet defined the new model. Conservative George Bush -- the conservationist, the rebuilder of New Orleans, the Mars explorer -- might soon find himself trapped in that same political no man's land. And after he retires back to his ranch on the mythical American frontier, this will be the terrain his successors inherit.

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Bruce Schulman is a professor of history at Boston University and the author of "The Seventies" (DaCapo).

Thinking big: At his Texas ranch last year, President Bush took his pickup to meet a visitor, Mexican President Vicente Fox.