NO SERIOUS person thinks that Afghanistan - remote, impoverished, barely qualifying as a nation-state - seriously matters to the United States. Yet with the war in its ninth year, the passions raised by the debate over how to proceed there are serious indeed. Afghanistan elicits such passions because people understand that in rendering his decision on Afghanistan, President Obama will declare himself on several much larger issues. In this sense, Afghanistan is a classic proxy war, with the main protagonists here in the United States.

The question of the moment, framed by the prowar camp, goes like this: Will the president approve the Afghanistan strategy proposed by his handpicked commander General Stanley McChrystal? Or will he reject that plan and accept defeat, thereby inviting the recurrence of 9/11 on an even larger scale? Yet within this camp the appeal of the McChrystal plan lies less in its intrinsic merits, which are exceedingly dubious, than in its implications.

If the president approves the McChrystal plan he will implicitly:

■ Anoint counterinsurgency - protracted campaigns of armed nation-building - as the new American way of war.

■ Embrace George W. Bush’s concept of open-ended war as the essential response to violent jihadism (even if the Obama White House has jettisoned the label “global war on terror’’).

■ Affirm that military might will remain the principal instrument for exercising American global leadership, as has been the case for decades.

Implementing the McChrystal plan will perpetuate the longstanding fundamentals of US national security policy: maintaining a global military presence, configuring US forces for global power projection, and employing those forces to intervene on a global basis. The McChrystal plan modestly updates these fundamentals to account for the lessons of 9/11 and Iraq, cultural awareness and sensitivity nudging aside advanced technology as the signature of American military power, for example. Yet at its core, the McChrystal plan aims to avert change. Its purpose - despite 9/11 and despite the failures of Iraq - is to preserve the status quo.

Hawks understand this. That’s why they are intent on framing the debate so narrowly - it’s either give McChrystal what he wants or accept abject defeat. It’s also why they insist that Obama needs to decide immediately.

Yet people in the antiwar camp also understand the stakes. Obama ran for the presidency promising change. The doves sense correctly that Obama’s decision on Afghanistan may well determine how much - if any - substantive change is in the offing.

If the president assents to McChrystal’s request, he will void his promise of change at least so far as national security policy is concerned. The Afghanistan war will continue until the end of his first term and probably beyond. It will consume hundreds of billions of dollars. It will result in hundreds or perhaps thousands more American combat deaths - costs that the hawks are loath to acknowledge.

As the fighting drags on from one year to the next, the engagement of US forces in armed nation-building projects in distant lands will become the new normalcy. Americans of all ages will come to accept war as a perpetual condition, as young Americans already do. That “keeping Americans safe’’ obliges the United States to seek, maintain, and exploit unambiguous military supremacy will become utterly uncontroversial.

If the Afghan war then becomes the consuming issue of Obama’s presidency - as Iraq became for his predecessor, as Vietnam did for Lyndon Johnson, and as Korea did for Harry Truman - the inevitable effect will be to compromise the prospects of reform more broadly.

At home and abroad, the president who advertised himself as an agent of change will instead have inadvertently erected barriers to change. As for the American people, they will be left to foot the bill.

This is a pivotal moment in US history. Americans owe it to themselves to be clear about what is at issue. That issue relates only tangentially relates to Al Qaeda, the Taliban, or the well-being of the Afghan people. The real question is whether “change’’ remains possible.

Andrew J. Bacevich is professor of history and international relations at Boston University. His new book “Washington Rules: America’s Path to Permanent War’’ is forthcoming.

© Copyright 2009 Globe Newspaper Company.