WASHINGTON (Reuters) - The Obama administration is routinely arguing against the release on bond of Central American women and children at a New Mexico detention center in a policy shift meant to discourage others like them from entering the United States, say lawyers for the detainees.

The lawyers, representing women and children being held at the detention center in Artesia, 170 miles (275 km) from El Paso, Texas, say the government has for the last two months routinely argued against granting bond.

In a July 15 affidavit obtained by Reuters, the Department of Homeland Security argues against their release. Lawyers representing the migrants say that since then, the affidavit has been submitted at nearly all bond hearings before immigration judges.

In the affidavit, Philip Miller, assistant director of Enforcement and Removal Operations, writes: "I have concluded that implementation of a 'no bond' or 'high bond' policy would significantly reduce the unlawful mass migration of Guatemalans, Hondurans and Salvadoran(s)."

Gillian Christensen, a spokeswoman for U.S. Immigration and Customs Enforcement, said on Thursday the administration feared that if the detainees were to be set free on bond, they might not show up for further deportation proceedings.

The New Mexico detention center is one of several set up to house women and children who have surged across the border to escape the rampant poverty and domestic- and gang-related violence of Guatemala, Honduras and El Salvador.

NO 'NO-BOND' POLICY-OFFICIAL

Department of Homeland Security Deputy Secretary Alejandro Mayorkas denied at a news conference on Tuesday that the department was uniformly opposed to the release of Artesia detainees.

"The authorities are implementing bond measures that are based on the individualized determination as well as a more macro appeal. There is not an across-the-board no-bond policy," Mayorkas said. He said the administration was reviewing its bond approach.

More than 66,000 parents traveling with their children have crossed the Southwest U.S. border in the 11 months ending Aug. 31, up from 12,908 over the same period the previous year. Women among these parents are held at Artesia with their children.

President Barack Obama has come under pressure from Hispanic American supporters who assail a policy of deporting Central Americans. Some have dubbed him "deporter in chief" and warned of the violence deportees will face on their return home.

Republicans favor strict measures and many of Obama's fellow Democrats fear any lifting of limits could hurt them with voters in congressional elections on Nov. 4. A Reuters/Ipsos poll last month found that 70 percent of Americans believed that immigrants threatened the country's beliefs and 63 percent that they burdened the economy.

When bonds are granted in Artesia, they are usually around $25,000, well above the national norm of $5,200, attorney Laura Lichter, who represents detainees in Artesia, said on Tuesday.

In the past migrants screened by Homeland Security agents within 72 hours who had no criminal record and proved a "credible fear" of returning home were released while building a case for asylum, but not anymore, lawyers for the detainees said.

Lichter cited the case of a woman client who fears returning to her home in El Salvador and suffers from gallstones that have gone untreated by doctors in the facility for more than a month. Though U.S. law dictates that immigrant detainees suffering from serious medical conditions be released, the woman has remained in detention, Lichter said.

"Remember, these are detainees without any criminal history, who have established that they have a winnable asylum claim, most of whom have relatives, friends or other support in the U.S. upon release," said Lichter. "This is unconscionable."

(Reporting by Julia Edwards; Additional reporting by Richard Cowan; Editing by Howard Goller)