Most analysts — of all political persuasions — have concluded the U.S. strategy in Afghanistan isn’t working and costs too much to be sustained much longer. Yet no one has produced a formula for a speedy exit that doesn’t risk chaos — or worse.

This leaves us stuck. President Obama has pledged to start pulling U.S. troops out of Afghanistan this summer, with an eye toward withdrawing most forces by 2014. But, in talks with U.S. and Afghan leaders and experts, I’ve yet to hear an exit plan that doesn’t risk returning Afghanistan to civil war and/or Taliban domination, while further destabilizing nuclear-armed Pakistan next door.

So I turned with interest to a much-touted book by military analyst Bing West with a promising title: “The Wrong War: Grit, Strategy, and the Way Out of Afghanistan.”

West is a Marine combat veteran who served as assistant secretary of defense in the Reagan administration. Unlike so many armchair military pundits, this 70-year-old embedded with dozens of frontline U.S. units in southern and eastern Afghanistan, humping up mountains and enduring firefights and dysentery. He writes in gripping prose about the heroic, but often thwarted, efforts of U.S. soldiers.

West says he believes our counterinsurgency strategy is failing, even though a surge of U.S. troops has pushed the Taliban back from its southern heartland, and U.S. Special Forces have shredded its midlevel command structure. The problem is political: Our troops can clear the Taliban, but the Afghan forces we’re training can’t hold the terrain, and President Hamid Karzai’s corrupt government can’t (or won’t) build up the country.

In a phone interview, West said: “When you put more Americans in there, there is progress. But what difference (will) it make when the Americans aren’t there?”

As for a solution, however, West offers only three pages at the end of a 300-page volume, confirming that it’s easier to describe the problem than come up with a comprehensive answer.

His plan in a nutshell: Cut back on expensive efforts to build up Afghanistan’s economic and democratic institutions. Focus mainly on building Afghan security forces. Remove half our 100,000 troops, and transition most of the rest into a tough adviser corps that embeds with and trains the Afghan army, backed by a large U.S. air presence. Then let the Afghans do their own fighting against the Taliban.

Of course, the Afghan army’s high illiteracy and attrition rates have undercut previous U.S. training efforts. Moreover, the army includes few ethnic Pashtuns from the south — the stronghold of the Pashtun Taliban — which gives it little credibility there.

West says he believes the Afghan army can still be shaped up, pointing to the 2010 battle for Marja, where U.S. Special Forces and a Marine support team embedded with an Afghan battalion and helped that unit fight well.

However, he says, to replicate this success story would require a dedicated U.S. Army and Marine adviser corps that pulled “the best officers from conventional battalions.”Do we really believe the Afghan army could achieve this level? Gen. David Petraeus has long argued it will find its legs only after the security situation is more stable, contending that if we leave too soon it might crumble altogether.

West concedes that, as U.S. combat troops exit, larger sections of the countryside are likely to fall under Taliban control. This is already happening in Nuristan and Kunar provinces where U.S. outposts have been shut down.

He says Kabul, and other large cities, wouldn’t fall to the Taliban: If the jihadis massed for attack, they could be stopped by U.S. airpower. I wonder how supply lines to the cities would be maintained if the Taliban controlled the outlying areas. Unless there is some kind of political deal with the Taliban, this scenario does not seem real.

Indeed, Karzai and U.S. officials now say there are preliminary talks with the Taliban about negotiations. But West dismisses the current prospects for such talks (for reasons I agree with).

“Negotiations ratify strength on the battlefield, not the other way around,” he writes. “Under current circumstances, negotiations do not offer … a safe way out of Afghanistan.”

So the Bing West formula is basically a gamble: that we can shape up the Afghan army, against all odds, even as our combat troops head for the exit. “Maybe I’m expressing a hope, not a reality,” says West bluntly. “Until we give it a test, we don’t know. That’s why our military is resisting testing this.”

His formula doesn’t differ that much from what I’m hearing from administration sources, who want Afghan troops to take on more responsibility soonest and hope talks with the Taliban will splinter its leadership and persuade some of them to make deals.

Obama will have to decide soon between these bad choices: leave most combat troops for another year, buying more time to weaken (or bargain with) the Taliban; or pull them sooner and pray that the Afghans can manage.

Neither choice looks promising. Like everyone else, I’m still looking for the magic option that doesn’t risk a Taliban takeover and a new civil war.