THOMAS GIBBONS-NEFF AND JULIAN E. BARNES

Jalil Rezayee/EPA, via Shutterstock

WASHINGTON — All American troops would withdraw from Afghanistan over the next three to five years under a new Pentagon plan being offered in peace negotiations that could lead to a government in Kabul that shares power with the Taliban.

The rest of the international force in Afghanistan would leave at the same time, after having mixed success in stabilizing the country since 2001. The plan is being discussed with European allies and was devised, in part, to appeal to President Trump, who has long expressed skepticism of enduring American roles in wars overseas.

The plan calls for cutting by half, in coming months, the 14,000 American troops currently in Afghanistan. It would task the 8,600 European and other international troops with training the Afghan military — a focus of the NATO mission for more than a decade — and largely shift American operations to counterterrorism strikes.

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Various elements of the plan were shared with The New York Times by more than a half-dozen current and former American and European officials. It intends to help talks with the Taliban that are being led by Zalmay Khalilzad, the American special envoy.

So far, the plan has been met with broad acceptance in Washington and NATO headquarters in Brussels. But American officials warned that Mr. Trump could upend the new plan at any time.

And officials said that even if the peace talks broke down, the United States would go forward with shifting to counterterrorism missions from training Afghan forces.

Until the final withdrawal, several thousand American forces would continue strikes against Al Qaeda and the Islamic State, including on partnered raids with Afghan commandos. The counterterrorism missions, and the military’s dwindling presence, are also critical to allowing the C.I.A. to operate in Afghanistan.

Lt. Col. Koné Faulkner, a Pentagon spokesman, said no decisions had been made as peace talks continued. The Defense Department “is considering all options of force numbers and disposition,” Colonel Faulkner said.

But European allies said they had been consulted about the proposal — a stark contrast to Mr. Trump’s surprise announcement in December to withdraw American forces from Syria.

“The Europeans are perfectly capable of conducting the training mission,” James Stavridis, a retired American admiral and former top NATO commander who is now with the Carlyle Group private equity firm. “It is a smart division of labor to have the United States shift the bulk of its effort toward the special forces mission and having the Europeans do the training mission.”

Mr. Stavridis said the two missions would be coordinated, including American logistical support and military backup for the European troops.

On Monday, American diplomats met with the Taliban in Qatar in the highest-level negotiations yet, including the attendance of Gen. Austin S. Miller, the commander of the international mission in Afghanistan. The negotiations paused on Wednesday and are set to resume on Saturday.

The two sides have sought to flesh out a framework agreement, decided in principle last month, for the full withdrawal of foreign troops and assurances by the Taliban to prevent terrorist groups that seek to attack the United States from using Afghan territory as a safe haven.

The Afghan government has not been a part of the negotiations because of Taliban reluctance to talk to President Ashraf Ghani or his envoys.

The prospect of an American military withdrawal has raised fears across the world that it could lead to the fall of the Western-backed government in Kabul and a return to the extremist rule of the Taliban. Before it was ousted in 2001, the Taliban was accused of human rights abuses, prohibited girls from attending school and imposed harsh penalties on accused heretics.

American officials have said any deal to withdraw international forces from Afghanistan must involve a cease-fire agreement and the inclusion of government leaders in the negotiations.

In a speech on Thursday in Kabul, Mr. Ghani warned Afghan security forces to be prepared for possible Taliban attacks ahead of any peace deal.

“Peace is not easy; it needs courage and bilateral honor,” Mr. Ghani said.

European officials have previously said they would rapidly pull their forces from Afghanistan if the American military was shorn too small to provide logistic support. American officials said enough troops would remain — even if they were cut to 7,000 — to continue the European training mission as outlined in the Pentagon’s plan.

In some respects, the focus on counterterrorism missions in Afghanistan is an endorsement of a plan by Vice President Joseph R. Biden Jr. as the Obama administration debated its own war strategy in 2009. Mr. Biden’s proposal was ultimately rejected in favor of a counterinsurgency plan, which called for training local forces and a surge of American troops, as pushed by Gen. Stanley A. McChrystal, who was then the top commander in Afghanistan.

Taliban negotiators deeply oppose the proposal for American counterterrorism troops to remain in Afghanistan for up to five years, and officials were unsure if a shorter period of time would be accepted by the militants’ rank and file.

Scaling back the training mission could leave the beleaguered Afghan military not just vulnerable to attacks, but at risk of fracturing. In January, Mr. Ghani announced that more than 45,000 Afghan troops had died since 2014; Pentagon officials have called their casualty numbers unsustainable.

Despite pouring billions of dollars into the Afghan military for more than a decade, Pentagon audits show that a renewed effort to modernize the fledgling Afghan Air Force will most likely not be self-sufficient until the mid-2030s.

Speaking to lawmakers in December, the incoming commander for American troops in the Middle East, Lt. Gen. Kenneth F. McKenzie Jr., said that Afghan forces could not sustain themselves without American and NATO support.

“I do know that today it would be very difficult for them to survive without our and our coalition partners’ assistance,” he said.

Current and former Defense Department officials said limiting American assistance to the Afghan military would require a delicate balance of providing just enough material support for the NATO training mission, known as Resolute Support, to ensure that Western allies remain invested without sacrificing counterterrorism operations.

European allies cited General Miller as describing the reduced troop levels as about “doing more with less.”

One former Defense Department official with knowledge of the talks said more American support for the training mission could be based outside Afghanistan and flown in when needed. European countries have relied heavily on American bases, supplies and other logistics throughout the war.

One German official, speaking on the condition of anonymity because of the sensitivity of the talks, underscored how reliant Berlin’s 1,300 troops are on medical evacuation aircraft and air support provided by the United States.

British forces may take part in counterterrorism operations, but those missions are expected to nearly completely be under American command.

Laurel Miller, who was a top State Department official working on Afghanistan and Pakistan policy during the Obama and Trump administrations, said it was risky to change the military mission in Afghanistan without a peace plan in place.

“The idea of scaling down to a small CT-only mission has long been discussed in the U.S. government,” she said. But, she said, “if you stop backing up Afghan forces in their main fight, you can’t very well keep working on your narrower priorities in isolation with Afghanistan falling apart around you.”

It is also possible that international funding support for the Afghan government could end up going to the Taliban under a power-sharing agreement. But American and European officials called it critically necessary to continue funding Afghan security forces.

The track record for American-supported governments after peace treaties or troop withdrawals is shaky at best.

American-trained South Vietnamese fell to Communist forces two years after the United States withdrew from the Vietnam War in 1973. Large portions of the Iraqi Army collapsed in the face of an Islamic State offensive in 2014, just three years after the withdrawal of the American military and its trainers, necessitating a return to Iraq by international forces.

Some officials believe continued funding for the Afghan military is more important than an enduring international troop presence for the survival of Afghanistan’s government.

“As long as we continue to provide funding to the Afghan security forces in the field, I think the security forces would be very capable of keeping order in the country, particularly in a scenario where the Taliban has come in from the cold,” Mr. Stavridis said.