KABUL, Afghanistan — A top NATO official said Wednesday that a complete handover of security to Afghan forces by 2014 was “”realistic, but not guaranteed,”” and the transition could last into 2015 “”or beyond.””

Mark Sedwill, NATO’s senior civilian representative in Afghanistan, cautioned that there could be “”levels of violence that are, by Western standards, pretty eye-watering”” even after 2014.

Sedwill spoke on the eve of a NATO summit in Lisbon, Portugal, at which the alliance is expected to agree on a framework for the eventual departure of international troops from Afghanistan, where they’ve been fighting for nine years.

His remarks appeared aimed at conditioning weary American and European publics to the likelihood that the transition won’t be clear-cut or inexpensive. They threw the end date for U.S. and other foreign combat forces further into question.

Aides to President Barack Obama now are playing down the deadline of July 2011, when the first U.S. troops are supposed to withdraw — at least according to Obama’s speech last December.

That date has long been a point of contention between the White House, which is trying to allay concerns at home, and the Pentagon, where officials say more time is needed to conduct a counterinsurgency strategy.

Sedwill said there had been a “”refocus of attention on 2014″” as the transition date.

In Washington, a defense official said the Obama administration recognized that NATO training and assistance would continue beyond 2014, but he said the training, advising and limited logistical support would be the major mission. The official spoke on the condition of anonymity because he wasn’t authorized to talk to reporters.

Under a classified campaign plan that Sedwill and military commander U.S. Gen. David Petraeus submitted in advance of the summit, the Afghan army and police assume control of security in most Afghan provinces four years from now. The process is supposed to begin in the first half of 2011.

The 2014 date, first suggested by Afghan President Hamid Karzai last year, “”is a goal. We’ve always been clear about that,”” Sedwill said. The report to NATO leaders says that date “”is realistic, but not guaranteed,”” he added.

Under the plan, international troops will move from partnering with Afghan forces to mentoring them to “”strategic overwatch”” from a distance, a pattern borrowed from the U.S. troop drawdown in Iraq.

Even after 2014, there may be regions in which Afghan forces aren’t in the lead, and troops of the NATO-led International Security Assistance Force will be on the streets, Sedwill said. “”That might last into 2015, or beyond.””

Some violence is also likely to continue, he predicted, saying it would be more criminal than political.

Obama deployed an additional 30,000 U.S. troops to Afghanistan earlier this year. Military officials say that the troop surge, a revised war strategy and stepped-up attacks on the Taliban-led insurgency have reversed the insurgency’s momentum.

“”The key judgment (in the classified report) is that we believe we are regaining the initiative. … It’s still clearly fragile. … But we believe in 2010 we have achieved what we wanted to. … We think we are in a different mode,”” Sedwill said.

He acknowledged that Karzai’s criticism, in a recent Washington Post interview, of stepped-up coalition “”night raids,”” aimed at seizing insurgents and arms, wasn’t helpful. “”I’d rather we be discussing these things privately,”” he said.

The envoy cautioned that U.S., European and allied nations would reap a “”dividend”” in terms of troops returning home and budget savings toward the end of the process. “”The transition dividend doesn’t come through on Day One,”” he said.