PHOENIX — Under pressure by animal welfare groups and many of his own people, the president of the Navajo Nation, Ben Shelly, has reversed his stance on horse slaughtering, saying he will no longer support it and will order the temporary suspension of the roundups of feral horses on the reservation.

The agreement, brokered by Bill Richardson, the former governor of New Mexico, is scheduled to be announced on Tuesday. One of its key provisions is to pressure the federal government to do more to help the Navajos handle the tens of thousands of horses that roam freely on their land. Mr. Shelly has estimated that feral horses cost the Navajos $200,000 a year in damage to property and range.

“I am interested in long-term humane solutions to manage our horse populations,” Mr. Shelly said. “Our land is precious to the Navajo people as are all the horses on the Navajo Nation. Horses are sacred animals to us.”

Mr. Shelly’s recalibrated position is sure to strengthen the arguments against horse slaughter in the nation, just as a legal fight to block the opening of horse slaughterhouses in New Mexico and Missouri reaches its final stages.