Israeli health officials said today that the mysterious illness that struck more than 300 Arab schoolgirls in the West Bank town of Jenin last week was largely the result of psychological rather than medical factors.

At a news conference in Tel Aviv, Dr. Baruch Modan, the director-general of the Israeli Health Ministry, said an investigation into the incident found no evidence that poison or other chemical substances caused the illness.

Modan attributed many of the cases to "hyperventilation" and described the spread of the illness as a "psychological and hysterical epidemic." He said the incident could have been triggered by anticipation of yesterday's observance of Land Day, an annual event in the West Bank and Arab sections of Israel to protest Israelis' confiscation of Arab land.

Several border policemen and two Israeli women soldiers also have complained of similar symptoms as the schoolgirls: headache, dizziness and nausea. It was not clear whether they also were believed to have suffered from a psychological reaction.

When reports of the illness first surfaced, Palestinians accused Israeli occupation authorities and Jewish settlers of planting poison in several Moslem schools for girls in the Jenin area. The Israelis, in turn, suggested that the epidemic was the work of Palestinians seeking to incite trouble in the West Bank in connection with Land Day.

At the same news conference today, Shlomo Ilya, the head of the Israeli civil administration in the West Bank, blamed "political agitators" seeking to disrupt "the quiet of Jenin" for the rapid spread of the illness.

A reporter for an Arabic-language daily was arrested late last night for allegedly getting into Jenin hospital and circulating among the girl victims telling them that they had been poisoned, Israeli military authorities said.

Israeli television said that the reporter, Kadura Moussa of the Jerusalem-based paper Al Fajr, disguised himself as a member of the hospital staff.

In addition, Hanna Siniora, editor-in-chief of Al Fajr, was arrested in his Jerusalem home late yesterday afternoon for reasons that still have not been made public. There was speculation that the arrest was connected with the Jenin epidemic, of which Al Fajr made a major issue.

Israeli officials said a total of 380 people, almost all of them Arab schoolgirls, became ill during the epidemic and that 106 remain under treatment in hospitals in the area.

The Associated Press quoted Health Ministry official Modan as saying that he wanted the Centers for Disease Control in Atlanta to verify the results of the inquiry. A spokeswoman for the centers said Thursday afternoon that no such request had been received from the Israeli government.

Meanwhile, military sources conceded tonight that an Arab youth whose body was found near Hebron yesterday died from a bullet wound. Palestinian sources said the youth, Dahsin Abdel Fatah Fatafteh, 18, was killed by Israeli security forces during a Land Day demonstration in the village of Tarkumiya.

The Israel Army's spokesman's office said yesterday after the body was found that the cause of death was not known. The spokesman's office said tonight that it still could not officially confirm that the youth died of a bullet wound and that an investigation was continuing.