A new report on targeted killing by C.I.A. drones in Pakistan’s tribal area concludes that the strikes have killed more civilians than American officials have acknowledged, alienated Pakistani public opinion and set a dangerous precedent under international law.

The report, by human rights researchers at the Stanford and New York University law schools, urges the United States to “conduct a fundamental re-evaluation of current targeted killing practices” including “short- and long-term costs and benefits.” It also calls on the administration to make public still-secret legal opinions justifying the strikes.

Human rights groups have previously reached similar conclusions, and the report draws heavily on previous reporting, notably by the Bureau for Investigative Journalism in London. But the study is among the most thorough on the subject to date and is based on interviews with people injured by drone-fired missiles, their family members, Pakistani officials, lawyers and journalists.

Research is difficult on the ground in Pakistan’s dangerous tribal regions, where militant groups are situated and most drone strikes occur, and the law school teams did not visit them. They did, however, meet in Pakistani cities with 69 people who had been injured in strikes, witnessed strikes or surveillance drones, or had relatives who were witnesses. The report includes excerpts from interviews with a dozen witnesses.

Sarah Knuckey, a veteran human rights investigator who led the N.Y.U. team, said she was particularly struck by the pervasive anxiety that residents of the tribal area described as a result of hearing drones buzzing overhead and knowing that a strike could come at any time. She said Pakistani journalists and humanitarian workers who work in the area described the same fear.

She also noted the pattern of second drone strikes after initial strikes, evidently targeting rescuers and relatives responding to a site. One humanitarian organization, which she said the authors agreed not to name for security reasons, told them its policy is to wait at least six hours after a drone strike before visiting the site.

American officials, including President Obama, have strongly defended the drone strikes, arguing that the remotely piloted aircraft are by far the most precise weapon for eliminating terrorists. They have said that both militants and Pakistani officials have exaggerated the number of civilian deaths.

Many experts on Al Qaeda believe that the strikes have hugely weakened the core Qaeda organization in Pakistan, though some believe that the backlash against the strikes has probably drawn some new recruits to the terrorist network. Many military experts support the government’s claim that using conventional airstrikes or troops on the ground to attack terrorist compounds would be likely to kill far more civilians than the drones have.

The full report, “Living Under Drones: Death, Injury and Trauma to Civilians from U.S. Drone Practices in Pakistan,” whose main authors are Ms. Knuckey, from N.Y.U., and James Cavallaro and Stephan Sonnenberg, of Stanford, and an accompanying video by the filmmaker Robert Greenwald, can be found here: livingunderdrones.org/.