(This story corrects the size of the reservation in the third paragraph)
By Laura Zuckerman
(Reuters) - The first effort of its kind to prevent wild horses roaming the Navajo Nation in the U.S. Southwest from being sent to slaughter in Mexico has gained the preliminary approval of tribal leaders, former New Mexico Governor Bill Richardson said on Thursday.
Under a draft agreement that still must be reviewed by the tribe, a foundation established by Richardson and actor Robert Redford would provide funds and expertise to the Navajo Nation to halt reservation roundups that have seen thousands of wild horses shipped to slaughterhouses in Mexico.
The impact of intensive grazing by wild horses in a high-desert reservation that spans more than 27,000 square miles (70,000 square km) of New Mexico, Arizona, Colorado and Utah has been compounded by drought and led to competition with livestock for sparse vegetation, said Rick Abasta, spokesman for Navajo Nation President Russell Begaye.
The roundups by the nation's agriculture department and the fate of the captured animals has ignited controversy among the tribe's more than 300,000 enrolled members, including wild horse advocates, Abasta said.
The issue has divided a tribal nation whose economy relies in part on free-range cattle and sheep but which also reveres horses.
"The Navajo elders have a saying which translates into English as 'Our horses are sacred,'" said Abasta.
Richardson, whose second term as New Mexico governor ended in 2011, said he and Redford formed the Foundation to Protect New Mexico Wildlife with the aim of aiding wild horses.
"Our main objective is to stop the roundups and stop the horse slaughter," said Richardson, who said Redford is a fellow horse enthusiast who owns a home in New Mexico.
Richardson said the agreement would first seek to identify the number of wild horses on the reservation, where estimates have ranged from several thousand to more than 70,000.
If ultimately approved, the deal, which proposes such methods as birth control to keep wild herds in check, would be the first of its kind on Indian lands and perhaps in the nation, he said.
"The Navajos are the biggest tribe in the country. If we strike an agreement here, it will set an example for other tribes that still slaughter," Richardson said.
Abasta said the nation's newly elected president is seeking feedback from tribal members.
"President Begaye wants a little more time to gather the input of grassroots organizations, ranchers and others to determine how best to go forward on implementing the agreement," he said.
(Reporting by Laura Zuckerman; Editing by Dan Whitcomb and Frances Kerry)