One in a series of occasional articles.

People who label the United States "imperialist" usually mean it as an insult. But in recent years a handful of conservative defense intellectuals have begun to argue that the United States is indeed acting in an imperialist fashion -- and that it should embrace the role.

When the Cold War ended just over a decade ago, these thinkers note, the United States actually expanded its global military presence. With the establishment over the last decade of a semi-permanent presence of about 20,000 troops in the Persian Gulf area, they contend, the United States is now a major military power in almost every region of the world -- the Mideast, Europe, East Asia and the Western Hemisphere. And even though the United States is unlikely to fight a major war anytime soon, they believe, it remains very active militarily around the globe, keeping the peace in Bosnia and Kosovo, garrisoning 37,000 troops in South Korea, patroling the skies of Iraq, and seeking to balance the rise of China.

The leading advocate of this idea of enforcing a new "Pax Americana" is Thomas Donnelly, deputy executive director of the Project for the New American Century, a Washington think tank that advocates a vigorous, expansionistic Reaganite foreign policy. In ways similar though not identical to the Roman and British empires, he argues, the United States is an empire of democracy or liberty -- it is not conquering land or establishing colonies, but it has a dominating global presence militarily, economically and culturally.

In some ways, the quiet debate over an imperial role goes to the basic question now facing American foreign policymakers: Was the military activism of President Bill Clinton -- from invading Haiti to keeping peace in Bosnia, missile attacks on Sudan and Afghanistan, and bombing Yugoslavia -- unique to his administration, or was it characteristic of the post-Cold War era, and so likely to be the shape of things to come?

The discussion of an American empire also helps illuminate the running battle for the last six months between Defense Secretary Donald H. Rumsfeld and his Joint Chiefs of Staff over how to change the U.S. military. The defense secretary wants to prepare the armed forces to deal with the threats of tomorrow, and so hints at cutting conventional forces to pay for new capabilities such as missile defense. But the Joint Chiefs respond that they are quite busy with today's missions.

Siding with the chiefs, Donnelly, a former journalist and congressional aide, argues that "policing the American perimeter in Europe, the Persian Gulf and East Asia will provide the main mission for the U.S. armed forces for decades to come." He contends that the Bush administration has tried to sidestep this reality, and instead is trying to formulate a more modest policy in the tradition of the "realist" or balance-of-power views associated with Henry Kissinger and Brent Scowcroft.

The Kissingerian course is mistaken, Donnelly says. He argues that the sooner the U.S. government recognizes that it is managing a new empire, the faster it can take steps to reshape its military, and its foreign policy, to fit that mission. Events of the last six months tend to support his argument: While Bush and his advisers talked during the presidential election campaign about withdrawing from peacekeeping missions in the Balkans, once in office they emphasized that they would not leave before European allies did, and they also faced the prospect of becoming more involved in a third Balkans mess, in Macedonia.

If Americans thought more clearly and openly about the necessity of an imperial mission, Donnelly argues, "We'd better understand the full range of tasks we want our military to do, from the Balkans-like constabulary missions to the no-fly zones [over Iraq] to maintaining enough big-war capacity" to hedge against the emergence of a major adversary.

Donnelly has few open supporters, even among conservatives. But he said he believes many people quietly agree with him. "There's not all that many people who will talk about it openly," he said. "It's discomforting to a lot of Americans. So they use code phrases like 'America is the sole superpower.' "

One of Donnelly's somewhat reluctant allies is Andrew Bacevich, a retired Army colonel who is a professor of international relations at Boston University. Bacevich does not much like the idea of an imperial America. But like it or not, he says, it is what we have.

"I would prefer a non-imperial America," Bacevich said in an e-mail interview. "Shorn of global responsibilities, a global military, and our preposterous expectations of remaking the world in our image, we would, I think, have a much better chance of keeping faith with the intentions and hopes of the Founders."

But he went on to dismiss that as wishful thinking. Rightly or wrongly, he said, maintaining American power globally already has become the unspoken basis of U.S. strategy. "In all of American public life there is hardly a single prominent figure who finds fault with the notion of the United States remaining the world's sole military superpower until the end of time," he wrote in the current issue of the National Interest, a conservative foreign policy journal that has been the major venue of the imperial debate.

So, Bacevich concluded, "The practical question is not whether or not we will be a global hegemon -- but what sort of hegemon we'll be."

Until American policymakers candidly acknowledge they are playing an imperial role on the world stage, Donnelly and Bacevich argue, U.S. strategy will be muddled, the American people frequently will be surprised by the resentment the United States meets overseas, and the military will not be given the resources necessary to carry out its missions -- such as more troops trained for a "constabulary" role of peacekeeping and suppressing minor attacks, along the lines of the 19th century British military.

But Donnelly and Bacevich split on the ultimate cost of taking an imperialist course. Like many critics of empire, such as conservative commentator Patrick J. Buchanan, who in 1999 wrote a book called "A Republic, Not an Empire," Bacevich worries that imperialism abroad could carry a high cost at home.

"Tom Donnelly sees all of that as really neat, exciting, return-of-the-Raj adventure," he said. "I see it as merely unavoidable, and suspect that we'll end up paying a higher cost, morally and materially, than we currently can imagine."

Donnelly responds that such concerns lack historical basis. He notes that as America has grown more powerful over the last 150 years, so too has it expanded domestic liberties, freeing its slaves and extending voting and other rights to women and minorities.

For an idea with so few public adherents, there are a surprising number of critics of taking up the imperialist burden. In a 1999 speech at the Council on Foreign Relations, for example, Samuel R. "Sandy" Berger, then Clinton's national security adviser, argued that "we are the first global power in history that is not an imperial power."

Many of the critics believe that embracing an imperial stance would backfire precisely because of the foreign reaction it would provoke, or maybe already is provoking. "People have got our number," said Chalmers Johnson, president of the Japan Policy Research Institute, an independent think tank outside San Diego. He believes that the United States is pursuing an imperialist course, and that "Coalitions are forming left and right around the world to thwart it." He points to closer cooperation between Russia and China, to a united Europe that is becoming less of an ally and more of a competitor, and to the swift rise of the anti-globalization movement. Last year, Johnson published a book titled "Blowback: The Costs and Consequences of American Empire." It was, he said, "ignored" in this country.

Joseph Nye, a former official in the Clinton-era Pentagon who is dean of Harvard's Kennedy School of Government, has just completed another book denouncing the idea. In "Soft Power: The Illusion of American Empire," to be published next year, he argues that the notion that the United States is, and should strive to remain, the world's only superpower has become widely accepted among conservative commentators.

Nye says this hegemonic view pays too much attention to military might. "I think that people who talk about 'benign hegemony' and 'accepting an imperial role' are focusing too much on one dimension of power and are neglecting the other forms of power -- economic and cultural and ideological," he said. Overemphasizing U.S. military strength, he continued, ultimately would undercut those less tangible forms of power, and so curtail any effort to maintain an empire.

Along the same lines, Richard Kohn, a University of North Carolina historian, argues that most Americans wisely would reject an imperial role if it were put to them openly. "The American people don't have the interest, the stomach or the perseverance to do it," Kohn said. "A few bloody noses and they'll want to pack it in. They recognize that it would cost us our soul, not to speak of the moral high ground -- in our own minds most of all."

To his critics, Donnelly responds that they are arguing with reality, not with him: "I think Americans have become used to running the world and would be very reluctant to give it up, if they realized there were a serious challenge to it."