CAMP PENDLETON — Involuntary manslaughter charges were dropped Friday against a 27-year-old Marine lance corporal who had faced trial in connection with the Marine killings of 24 civilians in Haditha, Iraq, in 2005.

Stephen B. Tatum, who also no longer faces charges of reckless endangerment and aggravated assault, will be compelled to testify in the court-martial of Staff Sgt. Frank Wuterich, his former squad leader.

Wuterich led the assault on two houses where most of the deaths occurred. Tatum's attorneys said their client, accused of killing two children in the incident, will testify but that no deal has been made with prosecutors about what he will say.

"It became clear to the experienced prosecution team that the right thing to do was dismiss all charges," Tatum's defense team, consisting of two civilian attorneys and two Marine attorneys, said in a statement.

Initially, murder charges were levied against four enlisted Marines in the shootings and four officers accused of not investigating properly. Tatum, of Edmond, Okla., is the third of the enlisted men to have charges dropped.

The civilians were killed after a Marine convoy was struck by a roadside bomb. One Marine was killed and two were injured.

Ordered to "clear" houses in a search for possible insurgents, Marines killed 19 civilians. Five others were killed outside, near their car. No evidence was found linking any of the dead to the roadside attack, prosecutors said.

Wuterich faces charges of voluntary manslaughter, aggravated assault, reckless endangerment, dereliction of duty and obstruction of justice. His court-martial has been delayed while evidentiary appeals are considered.

The decision to drop the charges against Tatum was approved by Lt. Gen. Samuel Helland, commander of the Marine Corps Forces Central Command. Tatum is a veteran of the battle in Fallouja in late 2004.

At a preliminary hearing, Tatum asserted in an unsworn statement that the light was so poor inside the houses that he saw only shapes and that he fired after hearing the racking of AK-47 assault rifles.

The hearing officer, calling the evidence against Tatum weak and unreliable, had recommended that charges be dropped. But the general overseeing the case rejected that recommendation in October and ordered Tatum to stand court-martial. If convicted, he could have faced 18 years in prison.