RENO, Nev. — A stampede of opposition is growing over a proposal by the U.S. Bureau of Land Management to kill or allow unrestricted sale of wild horses captured from western public land because of budget constraints.

Tens of thousands of horse advocates have voiced outrage at the idea of slaughtering what many revere as romantic symbols of the American West.

"Most Americans view these horses as the greatest symbols of our American freedom," said Ross Potter of Phoenix.

"If we kill them now without exhausting all other possibilities, we are telling the world that we have no respect for our own heritage," he said in a recent letter to the BLM. "I don't think that is an image we can afford to project."

The BLM's nine-member National Wild Horse and Burro Advisory Board is scheduled to consider the proposal at a meeting Monday in Reno.

About 33,000 wild horses roam the open range in 10 Western states, including Utah. The BLM has set a target "appropriate management level" of horses at 27,000.

Many critics say inept bureau management created the problem that has led to nearly as many horses being kept in long-term corrals as remain on the range.

Karen Sussman, president of the International Society for the Protection of Mustangs and Burros, said the BLM has never considered the health of herds when conducting roundups.

She and others say large-scale roundups upset a herd's social hierarchy, leading to unchecked breeding that threatens their gene pool and accelerates population growth.

"They are mandated by law to protect these horses for American citizens. They have not done that," she said.

"And now, on the backs of these horses that should never have been removed, they want to kill them."

Critics also argue that, when it comes to public land, wild horses get short shrift to the benefit of livestock and wildlife. They say that since 1971 about 20 million acres originally designated as herd areas have been withdrawn from that use. They say reopening those areas to horses would alleviate the need for boarding.

"While forage and water are rarely an issue for the established livestock and big-game interests, these same resources are almost always portrayed as being too little for the relatively tiny members of our nation's remaining wild horses and burros — who are too often scapegoated for ecological destruction caused ultimately by man," wrote Craig Downer, a wild-horse ecologist.

A report issued last week by the Government Accountability Office, the investigative arm of Congress, said the BLM needs to consider euthanizing horses or selling them to reduce spiraling costs of keeping them in long-term holding pens.

Wild horses and burros are protected under federal law. Most captured horses are placed for adoption, but those deemed too old or otherwise unadoptable are sent to long-term holding facilities — some for 15 to 20 years.

The BLM says demand for horses has declined, and the cost of caring for geriatric equines is devouring its budget.

The GAO report said costs of caring for wild horses likely will account for 74 percent of the program's overall budget this year, or more than $27 million. That percentage will climb, it said, unless alternatives are found.

Continuing current practices would require a budget of $58 million next year, escalating to $77 million in 2012, the BLM estimated.

The BLM already has authority to use euthanasia for horse management but has been reluctant to do for fear of public backlash.

"We have a responsibility to balance the budget, so we are going to have to make some tough choices," BLM Deputy Director Henri Bisson said when the proposal was first aired in June.

"We don't want to do this at the last minute. So we need to have a conversation with horse advocates and try to share the pain a little bit so people understand that if we have to make those tough changes it's not because we want to," he said.