By Joseph Ax

NEW YORK (Reuters) - A former supervising guard at New York City's Rikers Island, convicted of refusing to help a dying inmate at the troubled jail complex, convinced a judge to postpone sentencing on Thursday when he claimed at the last minute that his lawyer had not represented him properly.

Terrence Pendergrass, 51, was found guilty in December in New York of a federal civil rights crime for failing to summon medical assistance for Jason Echevarria, a mentally ill prisoner who died hours after swallowing a toxic "soap ball" used to clean cells.

Pendergrass, who faces up to 10 years in prison, was perhaps seconds away from hearing U.S. District Judge Ronnie Abrams impose his sentence when he claimed his lawyer, Sam Braverman, had not done a good job.

Until that point, the hearing had proceeded normally, including a statement from Echevarria's father, Ramon, who said he would never forgive Pendergrass.

"He is not a human being," Ramon Echevarria told Abrams. "Whatever he gets, he deserves."

Pendergrass also spoke, first apologizing to the Echevarria family for the pain they had suffered and claiming he would "never had done that to your son" if he had known Jason Echevarria was sick.

In a sometimes rambling monologue, however, Pendergrass then faulted Braverman for not introducing facts that might mitigate his potential sentence.

After a brief delay, Abrams reluctantly said she would appoint Pendergrass a new attorney on Friday and reschedule his sentencing, despite prosecutors' objection.

Braverman, an experienced defense attorney, declined to comment following the hearing.

Prosecutors said Pendergass dismissed warnings from two officers that Echevarria was ill on August 20, 2012, telling one not to bother him with "live, breathing bodies."

Later that evening, after a pharmacy technician expressed concern that Echevarria might die, Pendergrass again refused to summon assistance and ordered another officer not to do so, prosecutors said.

Echevarria was discovered dead the following morning.

Persistent reports of brutality against inmates and other civil rights violations at Rikers have prompted widespread calls for reform.

Manhattan U.S. Attorney Preet Bharara, whose office prosecuted Pendergrass, announced in December that the Justice Department would join an existing class-action lawsuit over prisoner abuse filed by the Legal Aid Society.

On Tuesday, the society filed another lawsuit on behalf of two female inmates who claimed a guard repeatedly raped them. The lawsuit asserts that sexual assault is widespread at the women's jail at Rikers and seeks class action status for all victims.

(Reporting by Joseph Ax; Editing by David Gregorio)