By Mike McDonald

GUATEMALA CITY (Reuters) - A session in the genocide trial of former Guatemalan dictator Efrain Rios Montt ended abruptly on Thursday, as his lawyers tried to suspend proceedings over a legal technicality and stormed out, leaving him sitting alone in court.

Rios Montt, 86, who ruled between 1982-83, was ordered to trial for genocide and crimes against humanity in January to answer for a counterinsurgency plan that killed more than 1,700 members of the Ixil indigenous group during the country's 1960-1996 civil war.

His lawyers argue that the judge who ordered the trial should not have presided over pre-trial hearings, but rather another judge, and are seeking to annul the proceedings.

"The debate must return to the (pre-trial) phase," defense lawyer Cesar Calderon said before walking out of the court. "We can't have two judicial processes at the same time. This trial must be annulled."

That left Rios Montt sitting alone in the courtroom without legal counsel. He tried to reach his lawyers by telephone, but got no answer. Then Judge Yasmin Barrios suggested he appoint a public defender, before calling off the day's hearing and ordering both sides to reconvene on Friday.

Prosecutors allege that Rios Montt, an army general before becoming dictator, turned a blind eye during the country's civil war as soldiers used rape, torture and arson to rid Guatemala of leftist insurgents.

His defense team has argued he had no control over battlefield operations and that genocide did not take place.

(Editing by Simon Gardner and Philip Barbara)