The estimate by Maj. Gen. Richard Barrons was a rare appraisal of the Taliban's fighting force, The Times of London reported.
Under the reconciliation program of the government of Afghan President Hamid Karzai, lower level Taliban fighters would be given jobs and other incentives and reintegrated into society if they give up their arms and cut any links with terror groups.
In his assessment of the Taliban strength, Barrons said: "There are probably 900 in the leadership, counting very junior to very senior, and there are between 25,000 and 36,000 people who would call themselves fighters."
"Some are ideological full-time jihadis; some are linked to the insurgency for localized reasons, local grievances; some because it's a way to make a living; some because they like to fight; some because their communities are hedging their bets between the government and the insurgency," the Times reported.
The general also said the Karzai government has not done much to earn its peoples' trust.
NATO's "reintegration cell," which the general runs, seeks to understand what motivates the militants to fight and the information is passed on to Afghan officials who use it to persuade the insurgents to change sides, the report said.
The reconciliation program is estimated to cost about $1 billion in the next five years.