ROME -- Italian prosecutors are investigating a U.S. soldier on possible homicide charges in connection with the shooting in Iraq of a senior Italian intelligence agent who was escorting a kidnap victim to safety, officials said yesterday.

The investigation has been in progress for several months but narrowed its focus yesterday on the single soldier who is believed to have fired all of the shots on the Italian car as it approached a Baghdad checkpoint, officials said.

In the March 4 incident, the Italian intelligence agent was killed and the rescued hostage, an Italian journalist, was wounded. The shooting became a major point of contention between the U.S. and Italy, one of only a handful in Europe to support the U.S. war in Iraq.

Italians were angered at the killing of Nicola Calipari, a well-respected major general in the military intelligence service. Thousands of people attended his funeral in Rome, where he was accorded top state honors and lauded as a national hero.

Italy and the United States launched a joint investigation into the nighttime shooting, but the two governments came away with very different conclusions. The United States cleared its soldiers of any wrongdoing and blamed the Italians for driving too fast on a dangerous road to the Baghdad airport and for failing to heed the soldiers' warnings to slow down.

But Italian investigators, relying on testimony from the driver and the journalist, Giuliana Sgrena, concluded the car was not speeding and there were no warnings from the American forces. The Italians blamed jittery soldiers, on one of their first days in Iraq, and the erection of an impromptu checkpoint that led to a fatal series of errors.

With the United States choosing to take no disciplinary action against the soldiers, Italian prosecutors launched a separate investigation. Yesterday, they narrowed their probe to the specific soldier who is believed to have done the shooting. He was identified in Italian court documents as Spc. Mario Lozano of the Army's New York National Guard. U.S. officials have refused to identify Spc. Lozano publicly, citing privacy issues.

The Italian investigation does not mean Spc. Lozano will be indicted, but it is a necessary step before further judicial action can be taken. Authorities are considering a charge of "voluntary homicide," roughly equivalent to a voluntary manslaughter charge in the U.S. system.