The Afghan government on Sunday identified 18 new areas where Afghan troops will soon take over security responsibilities from the NATO coalition, putting about half the country’s population under the lead of Afghan forces.

The security handover announced by President Hamid Karzai, ahead of an international conference on Afghanistan in Bonn, Germany, early next month, is the second phase of a gradual transition plan to have Afghan troops in control of the country by 2014, when the bulk of U.S. soldiers are expected to be gone.

The handover started with some of the most peaceful parts of Afghanistan. This round, however, includes some more-volatile areas. American officials have said they want to give Afghans control of difficult areas earlier in the process to allow time for training and support while there is still a large U.S. military presence.

By early next year, after these new areas have switched to Afghan control, the Afghan government will be in charge of eight of the country’s 34 provinces and several other cities and districts, including areas where the Taliban insurgency persists. The new provinces on the list are Nimruz, Daikundi, Samangan, Takhar and Balkh — none of which are focal points of the American military campaign. The provincial capitals of more-dangerous provinces, such as Ghazni, Wardak, and Nangahar, were also included.

The transition plan is risky, because Afghan security forces have not proved, in the most difficult areas, that they can prevail over the Taliban. Although the Afghan army has improved in recent years, it lacks the logistical capability to effectively maintain its equipment and arm its soldiers. The Afghan troops rely heavily on NATO for air support and the sophisticated technology to combat roadside bombs and other threats. The Afghan police continue to have problems with corruption and basic competence.

But U.S. and Afghan officials expressed optimism about the transition process and said the Afghan forces could handle the new responsibilities.

Gen. John R. Allen, the top American commander in Afghanistan, said in a statement that the Afghan forces have “made dramatic improvements in their development and effectiveness.”

“Transition is a reality, and it is a path for the future success of this country and the Afghan people,” Allen said.

Designating an area as being under Afghan control does not mean that coalition forces will leave, but rather that their role will shift toward a focus on training Afghan troops and backing them up if they need help.

Such arrangements differ in various parts of the country. But U.S. troops have also turned over bases to their Afghan counterparts, and they will continue to do so as more American soldiers depart.

Special correspondent Javed Hamdard contributed to this report.