In their final communique, the leaders also pledged funds for a plan aimed at persuading Taliban fighters to renounce violence - but offered no specific figures.
The meeting backed Afghan President Hamid Karzai's plan to reintegrate Taliban willing to "cut ties with al-Qaida and other terrorist groups and pursue their political goals peacefully."
It said handover of security responsibilities would begin this year, with the Afghan National Army "conducting the majority of operations in the insecure areas of Afghanistan within three years."
The conference was called to help world powers chart a roadmap out of Afghanistan amid rising U.S. and NATO casualties and falling public support.
The 70 nations say Karzai had promised to crack down on corruption and said a summit in Kabul later this year would offer specific plans to bolster his faltering government.
The text said discussions marked a "decisive step towards greater Afghan leadership to secure, stabilize and develop Afghanistan."
