WASHINGTON (Reuters) - Tens of thousands of children unaccompanied by parents or relatives are flooding across the southern U.S. border illegally, forcing the Obama administration and Congress to grapple with both a humanitarian crisis and a budget dilemma.

Boys lie down as they rest in bunk beds at the shelter for underage immigrants and repatriated minors "Mexico, my home" in Ciudad Juarez May 27, 2014. REUTERS/Jose Luis Gonzalez

An estimated 60,000 such children will pour into the United States this year, according to the administration, up from about 6,000 in 2011. Now, Washington is trying to figure out how to pay for their food, housing and transportation once they are taken into custody.

The flow is expected to grow. The number of unaccompanied, undocumented immigrants who are under 18 will likely double in 2015 to nearly 130,000 and cost U.S. taxpayers $2 billion, up from $868 million this year, according to administration estimates.

The shortage of housing for these children, some as young as 3, has already become so acute that an emergency shelter at Lackland Air Force Base in San Antonio, Texas, has been opened and can accommodate 1,000 of them, Homeland Security Secretary Jeh Johnson said in an interview with Reuters.

The issue is an added source of tension between Democrats and Republicans, who disagree on how to rewrite immigration laws. With comprehensive legislation stalled, President Barack Obama is looking at small, administrative steps he could take, which might be announced this summer. No details have been outlined but immigration groups are pressing him to take steps to keep families with children together.

The minors flooding over the border are often teenagers leaving behind poverty or violence in Mexico and other parts of Central America such as Honduras, El Salvador and Guatemala. They are sometimes seeking to reunite with a parent who is already in the United States, also without documentation.

“This is a humanitarian crisis and it requires a humanitarian response,” Senate Appropriations Committee Chairwoman Barbara Mikulski said in an interview. The Maryland Democrat, a former social worker, has likened the flood of unaccompanied children to the “boat people” of past exodus movements.

Senator Richard Shelby of Alabama, the senior Republican on Mikulski’s committee, said, “The need is there, you know the humanitarian aspect of it, but we’re challenged on money.”

Immigration groups lobbying for comprehensive reform argue that children are being hit hardest by the political deadlock.

BLAME GAME

With an even bigger funding challenge looming for 2015, Mikulski worries corners might be cut. She said children could end up being placed in federal holding cells meant only for adults and that funds might have to be shifted from other programs, such as refugee aid, to help cover the $252-per-day cost of detaining a child.

Mark Lagon, who coordinated the George W. Bush administration’s efforts to combat human trafficking, tied the sharp increase in unaccompanied minors to both U.S. economic factors and escalating violence in Central America.

He noted that there was a decrease in migration to the United States in the period 2008-2010 that reflected the U.S. economic downturn, and that has been reversed.

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“Now, it is again seen that there is a better life to be had in the United States and it’s worth the risk” of parents encouraging their children to make the perilous journey from countries like El Salvador and Honduras, said Langon, now a professor at Georgetown University and a senior fellow at the Council on Foreign Relations.

Also, with drug wars raging in Mexico, those fleeing Central American countries are less likely to make Mexico their destination and instead continue onto the United States, he said.

The budget and border-security implications of the problem could spill into campaigns for the November congressional elections, especially in Senate races in states with significant immigrant populations, such as North Carolina and Colorado.

Republican Representative John Carter of Texas blamed Obama for what he called a “nightmare at the border” with “tens of thousands of children” being smuggled into the United States.

In an opinion piece in The Hill newspaper last month, Carter said Obama’s policies had created an “invitational posture for illegal immigrants.” He said the administration helped to fuel the crossings with a 2012 decision to give temporary relief from deportation to certain children brought to the United States illegally by their parents.

Immigration advocacy groups point out that the unaccompanied youths coming to the United States since 2011 would not qualify under that program.

Lagon criticized the “political canard from my fellow Republicans” who suggest the tide of unaccompanied minors is the result of Obama policies, especially given Obama’s aggressive deportation policy since he became president in 2009.

A report by the UN High Commissioner for Refugees, based on interviews of 404 children aged 12-17 who left their home countries, found that 70 percent did so because of either domestic abuse, or violence “in the region by organized armed criminal actors, including drug cartels and gangs or by State actors.”

HARROWING JOURNEYS

Minors sometimes endure horrific conditions to get to the United States, immigration groups say.

Suyen G, who asked that her full name not be published, said she left her native Honduras two years ago aged 16 after securing $9,000 to pay a smuggler to get her into the United States. “I didn’t know it was illegal because a lot of people come. I thought it was something that normal people just do,” she said through a translator.

Suyen has a quick smile and looks like a typical American teenager in her sandals and fashionably-torn blue jeans. But she recounts a harrowing journey, saying she left home to escape a father who was beating her, and that along the way she was raped by a “coyote” or migrant smuggler. She endured 24 hours with no food as she sat atop a slow-moving freight train through Mexico and made an overnight trek by foot.

When she struggled to pull herself over a wall at the Mexico-U.S. border, Suyen said, “I thought I was going to die” after being shoved over by a coyote, plunging down the other side and landing atop a man below.

Unlike most kids, she entered the United States undetected, only to end up in a stranger’s house in Houston. There, she said she was forced to work without pay for a month before being transferred to a vineyard, where she cooked meals, also without pay, for 300 migrant workers. Reuters has not verified the details of her journey but Suyen told a similar story in a sworn deposition to an immigration court.

Finally, Suyen said, she was allowed to travel to northern Virginia where she was reunited with her mother.

Rebecca Walters, a lawyer in the northern Virginia office of Ayuda, which provides assistance to immigrants, helped Suyen win protective status and eventually a “green card” that allows her to work legally in the United States.

Walters said she typically juggles up to 60 cases at a time involving unaccompanied minors. A lot of her cases were boys who said they had friends who had been murdered for refusing to join gangs at home, she said.

Walters told of a boy from El Salvador who lived with an abusive, alcoholic father. The boy had to stop going outside to avoid getting beaten by gang members trying to recruit him.

In 2011, the boy and his brother, aged 16 and 15, arrived in the United States after walking for days in the desert. They were caught by U.S. authorities just inside border.

If not for the father’s abuse, “it would have been almost impossible” to prevent the brothers’ deportation, Walters said.

Minors who escape domestic abuse in their countries have a good chance of winning a special protective status from U.S. immigration courts, even if they are caught at the border. But the law does not recognize gang activity as a reason to protect immigrant children.