By GINGER THOMPSON
 
MEXICO CITY, March 24 - Defense Secretary Donald H. Rumsfeld announced Thursday that the United States would lift its ban on military aid to Guatemala, whose government has embarked on a major effort to change a military accused of kidnappings and massacres during more than 30 years of civil war.

"I've been impressed by the reforms that have been undertaken in the armed forces," Mr. Rumsfeld said at a joint news conference with President Óscar Berger of Guatemala. "I know it is a difficult thing to do but it's been done with professionalism and transparency."

Since taking office last year, President Berger has cut the military's troop strength by close to half, to 15,000 soldiers from 27,000. And he closed several bases that had been used to stage attacks against an armed insurgency.

Human rights investigations into the violence uncovered significant military atrocities, conducted under so-called scorched-earth policies. Some 200,000 people were killed or went missing in Guatemala from 1960 to 1996, mostly Mayan Indian civilians. A United Nations-backed truth commission found that 90 percent of those deaths were caused by the military.

The United States withdrew aid from Guatemala's military in 1990 after it was learned that soldiers were involved in the killing of an American named Michael Devine.

In the joint news conference in Guatemala City on Thursday, Mr. Berger assured Mr. Rumsfeld that such abuses had ended. "The shadow that was above our army has disappeared," he said. "Today we have a transparent army with half the personnel."

Human rights organizations denounced the move. Displaced soldiers, they said, had joined powerful criminal organizations that smuggle drugs and weapons through Guatemala.

Adriana Beltrán, an expert on Guatemala with the Washington Office on Latin America, a research institution, said Mr. Berger's government had done very little to stop private groups of gunmen from intimidating and killing people who were working to uncover past and present human rights abuses in Guatemala. Rewarding the government with arms sends the wrong message, she said.