CIUDAD HIDALGO, Mexico » With her leg snapped and folded excruciatingly over her shoulder, Elvira Lopez HernC!ndez lay flat on a railroad bed as the freight train hurtled above her, clinging tightly to two things: the railroad ties beneath her and the memory of the 4-year-old daughter she had left behind in Guatemala.

"I said: ‘My God, I don’t want to die! My daughter!"’

She slipped off the train in January, one of scores of migrant stowaways heading to the United States. Now she sat at a shelter here, an amputee. But she had no intention of returning to the crime and desperation of Guatemala City; she was still looking north.

"What can I do?" she said.

In Washington, the biggest immigration overhaul in decades would tighten border security between Mexico and the United States to stem the flow of illegal crossings.

But there is another border making the task all the more challenging: Mexico’s porous boundary with Central America, where an increasing number of migrants heading to the United States cross freely into Mexico under the gaze of the Mexican authorities. So many Central Americans are fleeing the violence, crime and economic stagnation of their homes that U.S. authorities have encountered a tremendous spike in migrants making their way through Mexico to the United States.

U.S. arrests of illegal crossers from countries other than Mexico — mostly from Honduras, Guatemala and El Salvador — more than doubled along the southwest border of the United States last year, to 94,532 from 46,997 in 2011.

Janet Napolitano, the secretary of homeland security, met with Mexican officials in January, partly to discuss improving security on Mexico’s border with its Central American neighbors, something the new president, Enrique Pena Nieto, has promised to do. The United States, which has provided equipment and other assistance to help shore up Mexico’s southern border, has long worried about migrants, drugs, guns and possibly even terrorists heading north, concerns shared by Mexico.

But Mexico has been conflicted about its border. Many here see migrants as Latin American brethren who need humanitarian assistance as they pass through on their journey north. Yet there is also growing concern that migrants may stay longer in Mexico as its economy picks up and it becomes harder to cross into the United States.

Here in Ciudad Hidalgo, a police officer watched on a riverbank as seven men crossed the narrow Suchiate River separating this part of Guatemala and Mexico. They sat on a makeshift raft of wooden planks and giant inflatable inner tubes, one of scores openly crossing back and forth carrying beer, paper towels, fruit, soft drinks and, of course, migrants heading to the United States.

The officer saw the men, dressed in tattered clothes and carrying backpacks, hop off the raft and drift into town. He did not stop or question them.

"If they are without papers, we would have to house and feed them until the immigration authorities come," he said. "We don’t have a budget for that."

The migrants from Central America speak of needing work — like previous generations. But they also talk about out-of-control crime in big cities, as drug and organized crime groups from Mexico push into their countries.

Few had even heard about the debate to overhaul immigration laws and possibly open a pathway to citizenship for immigrants living illegally in the United States. Instead, the prevailing force seems to be deteriorating conditions at home.

Lopez Hernandez said neighbors had been kidnapped for ransom. One young man from Honduras hung his head as he recalled a brother gunned down. Another said he could never imagine returning to Honduras after being shot in the gut and seeing his sister’s arms chopped off by a man who invaded a party looking for a gang rival.

"Everybody wants to get out," said another migrant from Honduras, Joel Bunes, 21.

The United States has poured money into Honduras, El Salvador and Guatemala to train and aid their police, but violence remains disturbingly high, raising vexing questions.

How far should the United States go in pressing Mexico to secure its free-for-all border? To what extent should the United States help alleviate the economic woes and instability driving migrants out of Central America, especially in cities like San Pedro Sula, Honduras, often called the murder capital of the world?

Next week, President Barack Obama will attend a meeting with Central American presidents, who have said they want to discuss migration and improving the economy and public safety with him.

"This is a truly regional problem and needs regional decisions and even regional institutions to resolve, and the U.S. could play a larger role in developing that," said Eduardo Stein, a former vice president of Guatemala who studies migration.

U.S. Customs and Border Protection said it planned to run public service announcements in Central America warning of the dangers of making the crossing. Migrants face robbers, rapists, crooked police officers and inhospitable terrain; disappearances are common.

Mexico says it is doing its part, spending about $300 million in the past few years building or modernizing border crossings, issuing identity cards for agriculture workers and establishing checkpoints on major roads to deter and catch migrants.

Yet on a recent afternoon, half of the eight checkpoints on a major highway heading north were unattended or staffed by officials paying only minimal attention. At one crossing at the Suchiate River, beneath a bridge, smugglers and migrants passed literally under the noses of customs and immigration officers above.

At a migrant shelter in Tapachula, young men from Honduras huddled around a map on a wall, placing one finger on Honduras and another on the United States.

"My God, we are not even halfway there," one said.

Selvin Espinoza, 19, said the group had been robbed along the way by police officers in Guatemala who demanded nearly $100 for safe passage.

But factory jobs back home were drying up, Espinoza said, while gangs roamed, kidnapping and extorting at will.

"You cannot make enough to make ends meet," he said.

Outside the shelter, a smuggler from El Salvador waited for them, recruiting more customers for the journey north.

"I know how to get them to the train north or on the buses," he said.

Just north, in Arriaga, migrants gathered where the train, known as the Beast, departs for northern cities. A Panamanian bought soda as Guatemalans pooled their money for tortillas and Hondurans gathered around a pickup truck where church workers offered coffee and pastries.

Everybody knew of the danger of the train; nobody spoke of skipping it.

"I am afraid of the train, but it is something you have to do," said one.

Lopez Hernandez knows it well. Her husband died four years ago, leaving her a widow at age 18 with a 9-month-old girl.

Unable to find work, she said, she decided to join a brother who had made it to Florida a few years before. He assured her there were jobs as maids, cooks, baby sitters, and she hoped to earn enough money to support her daughter and the relatives caring for her back home.

She made it to Mexico and onto the train. But after it departed there were cries of "Migra!" — the immigration police — and a scramble that sent her tumbling under the train.

"I closed my eyes and bore the pain," she said.

Eddie Ventura, 31, a Guatemalan, stood on the bridge across the Suchiate River on the Guatemalan side, selling disposable razors for $1 apiece. His own prosthetic leg, an old donated one, rested against a railing; he had lost his leg, like Lopez Hernandez, after falling from the train, and now he watches his compatriots take their chances.

"They don’t know what is waiting for them," Ventura said, shaking his head.

Yet he has not given up trying himself.

"I still want to get into that country," he said of the United States.

© 2013 The New York Times Company