A study by an Israeli psychologist into the violent behaviour of the country's soldiers is provoking bitter controversy and has awakened urgent questions about the way the army conducts itself in the Gaza Strip and West Bank.

Nufar Yishai-Karin, a clinical psychologist at the Hebrew University in Jerusalem, interviewed 21 Israeli soldiers and heard confessions of frequent brutal assaults against Palestinians, aggravated by poor training and discipline. In her recently published report, co-authored by Professor Yoel Elizur, Yishai-Karin details a series of violent incidents, including the beating of a four-year-old boy by an officer.

The report, although dealing with the experience of soldiers in the 1990s, has triggered an impassioned debate in Israel, where it was published in an abbreviated form in the newspaper Haaretz last month. According to Yishai Karin: 'At one point or another of their service, the majority of the interviewees enjoyed violence. They enjoyed the violence because it broke the routine and they liked the destruction and the chaos. They also enjoyed the feeling of power in the violence and the sense of danger.'

In the words of one soldier: 'The truth? When there is chaos, I like it. That's when I enjoy it. It's like a drug. If I don't go into Rafah, and if there isn't some kind of riot once in some weeks, I go nuts.'

Another explained: 'The most important thing is that it removes the burden of the law from you. You feel that you are the law. You are the law. You are the one who decides... As though from the moment you leave the place that is called Eretz Yisrael [the Land of Israel] and go through the Erez checkpoint into the Gaza Strip, you are the law. You are God.'

The soldiers described dozens of incidents of extreme violence. One recalled an incident when a Palestinian was shot for no reason and left on the street. 'We were in a weapons carrier when this guy, around 25, passed by in the street and, just like that, for no reason - he didn't throw a stone, did nothing - bang, a bullet in the stomach, he shot him in the stomach and the guy is dying on the pavement and we keep going, apathetic. No one gave him a second look,' he said.

The soldiers developed a mentality in which they would use physical violence to deter Palestinians from abusing them. One described beating women. 'With women I have no problem. With women, one threw a clog at me and I kicked her here [pointing to the crotch], I broke everything there. She can't have children. Next time she won't throw clogs at me. When one of them [a woman] spat at me, I gave her the rifle butt in the face. She doesn't have what to spit with any more.'

Yishai-Karin found that the soldiers were exposed to violence against Palestinians from as early as their first weeks of basic training. On one occasion, the soldiers were escorting some arrested Palestinians. The arrested men were made to sit on the floor of the bus. They had been taken from their beds and were barely clothed, even though the temperature was below zero. The new recruits trampled on the Palestinians and then proceeded to beat them for the whole of the journey. They opened the bus windows and poured water on the arrested men.

The disclosure of the report in the Israeli media has occasioned a remarkable response. In letters responding to the recollections, writers have focused on both the present and past experience of Israeli soldiers to ask troubling questions that have probed the legitimacy of the actions of the Israeli Defence Forces.

The study and the reactions to it have marked a sharp change in the way Israelis regard their period of military service - particularly in the occupied territories - which has been reflected in the increasing levels of conscientious objection and draft-dodging.

The debate has contrasted sharply with an Israeli army where new recruits are taught that they are joining 'the most ethical army in the world' - a refrain that is echoed throughout Israeli society. In its doctrine, published on its website, the Israeli army emphasises human dignity. 'The Israeli army and its soldiers are obligated to protect human dignity. Every human being is of value regardless of his or her origin, religion, nationality, gender, status or position.'

However, the Israeli army, like other armies, has found it difficult to maintain these values beyond the classroom. The first intifada, which began in 1987, before the wave of suicide bombings, was markedly different to the violence of the second intifada, and its main events were popular demonstrations with stone-throwing.

Yishai-Karin, in an interview with Haaretz, described how her research came out of her own experience as a soldier at an army base in Rafah in the Gaza Strip. She interviewed 18 ordinary soldiers and three officers whom she had served with in Gaza. The soldiers described how the violence was encouraged by some commanders. One soldier recalled: 'After two months in Rafah, a [new] commanding officer arrived... So we do a first patrol with him. It's 6am, Rafah is under curfew, there isn't so much as a dog in the streets. Only a little boy of four playing in the sand. He is building a castle in his yard. He [the officer] suddenly starts running and we all run with him. He was from the combat engineers.

'He grabbed the boy. I am a degenerate if I am not telling you the truth. He broke his hand here at the wrist, broke his leg here. And started to stomp on his stomach, three times, and left. We are all there, jaws dropping, looking at him in shock...

'The next day I go out with him on another patrol, and the soldiers are already starting to do the same thing."

Yishai-Karin concluded that the main reason for the soldiers' violence was a lack of training. She found that the soldiers did not know what was expected of them and therefore were free to develop their own way of behaviour. The longer a unit was left in the field, the more violent it became. The Israeli soldiers, she concluded, had a level of violence which is universal across all nations and cultures. If they are allowed to operate in difficult circumstances, such as in Gaza and the West Bank, without training and proper supervision, the violence is bound to come out.

A spokeswoman for the Israeli army said that, if a soldier deviates from the army's norms, they could be investigated by the military police or face criminal investigation.

She said: 'It should be noted that since the events described in Nufar Yishai-Karin's research the number of ethical violations by IDF soldiers involving the Palestinian population has consistently dropped. This trend has continued in the last few years.'