Once upon a time, Afghanistan was the forgotten war in Washington. Not anymore.

As President Obama prepares to decide the size and tempo of the drawdown of US forces from Afghanistan that he says will start by the end of July, members of Congress and prominent think tanks are issuing starkly divergent demands and recommendations.

The superlatives and warnings of dire consequences that both sides have used to discuss a large and precipitous withdrawal of US troops are all the more striking, considering that the decade-long Afghanistan war carried on in the shadow of the Iraq war and other conflicts for most of those years.

On Wednesday, a group of 27 senators organized by two Democrats and a Republican sent a letter to Mr. Obama demanding a “sizable and sustained” reduction in the 103,000 US troops in Afghanistan.

Also on Wednesday, Sen. Lindsey Graham (R) of South Carolina took the opposite position in a Washington speech, saying that leaving Afghanistan too quickly would be the "biggest [foreign policy] mistake we have made in my lifetime."

Obama has committed with America’s NATO partners to keeping some US forces in Afghanistan until 2014. But in the aftermath of the successful Osama bin Laden operation in Pakistan, and with Congress looking for ways to cut back on spending, the $2-billion-a-week Afghanistan war is increasingly in the sights of federal budget cutters.

White House officials say Obama is waiting for the assessments of his commanders on the ground before making any decisions, but they confirm that the cost issue is weighing heavily.

In their letter to Obama, the senators laud US forces for successfully removing the Taliban government that allowed Afghanistan to become a haven for Al Qaeda. But nearly a decade after that objective was secured, the war’s cost “far outweighs the benefits,” they say. “It is time for the United States to shift course in Afghanistan,” they add.

That theme of shifting course in the war is increasingly favored by officials who have soured on the manpower-heavy and costly counterinsurgency strategy that was behind Obama’s surge of 30,000 troops last year.

In an opinion piece Wednesday for the Wilmington News Journal in his home state, Sen. Chris Coons (D) of Delaware called the current counterinsurgency strategy in Afghanistan “unsustainable.” Instead, he said, the drawdown to begin next month should “mark the beginning of a new, more targeted counterterrorism strategy that more wisely focuses our military and diplomatic resources on defending America’s security interests.”

The Afghanistan debate has also surged to the forefront among Washington’s think tanks. On Monday, the liberal-leaning Center for American Progress issued a report calling on Obama to start the Afghanistan drawdown by pulling out at least 15,000 troops quickly, with the goal of falling to 40,000 by the end of 2012.

At the neoconservative-favoring American Enterprise Institute – one of the architects of President Bush’s surge of troops in Iraq, and a bastion of support for Obama’s surge – military and security experts use terms like “disaster” to describe any precipitous drawdown.

Republicans have at times been stronger supporters of Obama’s Afghanistan policy than members of his own party. But GOP support for a boots-on-the-ground war is starting to show cracks, especially when the cost of keeping a soldier in Afghanistan has reached $1 million a year.

In addition to the two Republican senators who signed the senators’ letter to Obama – Mike Lee of Utah and Rand Paul of Kentucky – GOP presidential aspirant Mitt Romney caused a few waves when he declared in a Republican debate Monday night that Afghanistan is a “war for independence” that US soldiers should not be fighting.

“One lesson we’ve learned in Afghanistan is that Americans cannot fight another nation’s war of independence,” Mr. Romney declared to some shocked Republicans. “Only the Afghanis can win Afghanistan’s independence from the Taliban.”

Senator Graham – who supported John McCain over Romney in the 2008 Republican presidential contest – quickly skewered Romney’s comment as suggestive of a “Jimmy Carter” (read weak-kneed) foreign policy. And Sen. James Inhofe (R) of Oklahoma accused Romney of trying to appeal to America’s isolationist vein.

• David Grant in Washington contributed to this story.