Among the many reasons: It is not clear that the Taliban want to negotiate, or who even represents the organization. The Afghan president has distanced himself from the talks, raising doubts about whether the country?s leaders would be open to a reprise of Taliban involvement in the political process.

And Pakistan, the vital third leg of negotiations because of its ties to the Taliban, is increasingly a wild card because of recent strains with the United States over the drone assaults on terrorist suspects inside Pakistan.

Mr. Obama told soldiers at Fort Drum, N.Y., on Thursday that ?because of you, there are signs that the Taliban may be interested in figuring out a political settlement, which ultimately is going to be critical for consolidating that country.?

So far, however, those signs are hazy at best, according to officials and diplomats.

American officials have participated in three meetings this year with an English-speaking Afghan who was once a personal assistant to the renegade Taliban leader Mullah Muhammad Omar. Those meetings, in Germany and Qatar, appear to have accomplished little more than confirming the man?s identity, and perhaps not even that, according to officials familiar with the talks, all of whom requested anonymity to discuss the secret talks.

Adding another layer of complexity to the already murky effort, the English-speaking Afghan, Tayeb Agha, who was an aide to Mullah Omar during the Taliban?s rise to power, was arrested by Pakistani authorities last year and then released, leading American officials to assume that he is negotiating on behalf of the Taliban with the blessings of the Pakistani authorities.

?We?re at that stage where it?s very confusing,? one senior administration official said, adding that the meetings could not even be called ?talks? at this stage, let alone ?peace talks.?

The wariness in part reflects the fact that the administration has been badly embarrassed by previous diplomatic efforts. An Afghan was given substantial sums of cash last year and was flown on a NATO aircraft in the belief that he was a Taliban envoy, but he turned out to be an impostor.

Even so, the renewed diplomatic push signals a significant shift in Mr. Obama?s strategy since he came to office in 2009 and increased American forces in Afghanistan to nearly 100,000 troops, from 34,000, in an effort to crush a resurgent Taliban insurgency.

While the military has secured parts of the country and bolstered the Afghan government?s security forces, the administration now recognizes that a final American withdrawal depends on a political settlement with the Taliban, a fundamentalist Islamic movement equated closely with the murderous ideology of Al Qaeda. The attacks of Sept. 11, 2001, were orchestrated by Al Qaeda under the Taliban?s protection.

The administration has imposed significant conditions for any reconciliation with the Taliban. The movement?s leaders must disarm, sever ties with Al Qaeda?s remaining leadership, recognize the government in Afghanistan and accept the country?s Constitution, including basic rights for women, who were severely repressed when the Taliban governed the country in the 1990s.

It is uncertain whether the Taliban or even parts of its leadership are willing to accept such conditions, and many experts are deeply skeptical.

?There really can?t be a deal on the core red lines, because that?s what red lines are,? Michael O?Hanlon, a senior fellow at the Brookings Institution, said of the conditions, using the diplomatic term for nonnegotiable demands.

The diplomatic effort is being led by Marc Grossman, who replaced Richard C. Holbrooke as special envoy to Afghanistan and Pakistan after Mr. Holbrooke died in December.

Thom Shanker contributed reporting.