One moment, Pedro Velazquez was standing on the roof of the partially built townhouse, preparing to anchor his harness to the top. The next, he was careening downward, grasping in panic for a handhold as he sailed over the edge toward the frozen ground four stories below.

At the Maryland Shock Trauma Center, doctors surveyed the damage: Smashed wrist. Broken leg. Fractured spine. Shattered dream.

"All I could think of was my wife and my children in Mexico," the 43-year-old roofer recalled in Spanish recently, blinking back tears as he sat in a sterile nursing home room in Manassas. "What will they live on without me to support them?"

Like many of the Latino immigrants who have swelled the nation's workforce over the past decade, Velazquez was drawn by the prospect of a booming economy and plentiful jobs, settling illegally in Dale City less than a year before his accident in February.

Now, paralyzed from the chest down and unable to use his lower arms and hands, he has joined the growing ranks of a different class of newcomer: one of the thousands of immigrant Latino men -- both documented and undocumented -- who are injured or killed while working in the United States each year.

According to authors of a study to be released soon by the National Academy of Sciences, foreign-born Latino men are now nearly 2 1/2 times more likely to be killed on the job than the average U.S. worker.

Government statistics on nonfatal injuries are less revealing because they lump immigrants together with American-born Hispanics, who tend to have more education and better language skills. Yet here, too, the news is grim, with Hispanic men about 50 percent more likely to be injured than the average worker.

And under the laws of many states, employees who are in the country illegally are ineligible for full medical coverage or monetary compensation for their injuries. Instead, they must depend on emergency rooms or simply forgo medical care.

"Our nation is being built on the backs of these guys," said Daniel P. Barrera, a lawyer who has helped Velazquez and other injured Latinos in the area navigate the workers' compensation system. "It's really unfair that they're being treated this way when they're hurt."

Researchers are trying to determine all the reasons behind the rise in injuries, but one is clear: Often minimally educated and desperately poor, Latino immigrants have flocked to some of the nation's most dangerous industries in record numbers, eagerly snapping up nonunion construction, manufacturing and agricultural jobs that are too low-paying and high-risk to attract enough U.S.-born workers.

Largely as a result, the number of fatally injured Latino workers rose by more than 50 percent -- from 533 in 1992 to 815 in 2000 -- even as the nation's non-Hispanic fatality rate dropped.

Among the latest to be added to the tally were two Hispanic steelworkers from North Carolina who were killed in Rockville last month when a concrete parking garage they were building collapsed on top of them. A non-Hispanic worker was also killed, and another Hispanic worker was seriously injured.

In the greater Washington area, where Latinos make up 8 percent of approximately 5.4 million residents, the walking wounded increasingly fill the waiting rooms of rehabilitation clinics. Prompted by an explosion in its Hispanic clientele three years ago, one of the region's largest injury-treatment centers, Rehab at Work, opened an office in Alexandria with four Spanish-speaking therapists.

And at the Shady Grove offices of another group, Rehabilitation Services of Greater Washington, occupational therapist Rich Shegogue said he spends much of his day speaking Spanish.

A recent visit to that clinic amounted to a tour of the underside of the American Dream.

At one table, Mexican-born Mario Perez -- whose right pinkie tendon was sliced by a falling piece of plasterboard -- winced in pain as a therapist massaged his hand.

Nearby, Peruvian-born Luis Enrique Bonta waited his turn, distractedly rubbing the stumps of three fingers he lost in a printing press accident.

The psychological damage to such workers can be tougher to cure than their physical disabilities, Shegogue said.

"Because of the machismo ideal in Hispanic culture, it's a very heavy blow for our Latino clients to be told they can't work," he said. "I see a lot of frustration and depression stemming from that."

Bonta said he has struggled with both. "My family is really feeling the change in my character," said the 46-year-old, who lives with his wife and two of his children in Gaithersburg. "I'm in pain all the time and bothered by everything. And I don't want to do anything anymore. I just feel so impotent."

Yet for all their difficulties, Shegogue's clients are at least getting medical care and financial assistance for their injuries. That can be a challenge when an injured worker is one of the nation's estimated 7 million to 8 million illegal immigrants.

While many states do not distinguish between documented and undocumented immigrants when it comes to workers' compensation, plenty do. The most extreme is Wyoming, where undocumented immigrants are excluded from all compensation. Virginia's Supreme Court held the same in a 1999 decision, prompting the state legislature to pass a law extending most medical and wage benefits to illegal immigrants the following year.

Even so, in Virginia, Maryland and the District, undocumented workers are not eligible for vocational retraining if their injuries prevent them from doing their original jobs.

And while Virginia and Maryland do allow undocumented workers financial compensation for permanent disabilities, such workers cannot receive compensation from employers for a temporary loss in wages they experience if they can only do light work while recovering.

That was devastating news to a Bolivian-born construction worker living in Virginia whose hand was crushed by a plummeting scaffolding plank last year.

The worker, who asked that his name be withheld because he is undocumented, received no compensation during the roughly six months he was recuperating from the accident. As a result, he said, he was forced to exhaust his savings to pay his share of the apartment he rents with five other laborers.

Worst of all, he said, was the knowledge that his wife and three children back in Bolivia -- to whom he used to send about $1,000 a month -- were having to get by on much less.

"They used to eat meat once a week. Now they can't afford it," he said.

Steven Camarota, director of research at the Center for Immigration Studies, said he has some sympathy for such immigrants.

Nonetheless, he noted, "these folks are in the country knowingly and willingly violating our immigration laws. . . . And the more you extend benefits to them, the more you normalize their presence and convey to them, to their employer and to people thinking about coming here illegally that the United States simply isn't serious about its immigration laws."

Lawyers for such workers counter that illegal employees should not have to suffer while the companies that employ them -- often at lower wages than legal workers -- get a free pass.

Immigrant advocates also speculate that undocumented workers face greater chance of injury because the companies that are willing to risk hiring them may be more likely to reduce costs by cutting corners on safety.

"The employer's calculus is that these are workers who won't raise issues of health and safety because they either don't know they can, or will be afraid of losing their job and getting deported," said Brian Christopher, executive director of the Alice Hamilton Center, a nonprofit work-safety training center in Silver Spring.

Unscrupulous employers also may fail to inform immigrant workers of their rights under the compensation system or neglect to obtain legally required workers' compensation insurance, immigrant advocates said.

The latter can be a particularly thorny problem for workers in the District, where it can take a year or more to get compensation from a special fund for workers at uninsured companies.

Eric May, a lawyer based in the District, said he recently had to turn down a house cleaner seeking compensation from a janitorial company for injuries she suffered in an accident while driving from one job to another in the firm's vehicle.

"From what I could tell, the employer wasn't insured, so it would have been too long and arduous a process to come to the woman's rescue," May said.

Even when employers are insured, they may contest an employee's claim in court, causing long delays during which immigrant workers who cannot afford to pay for treatment out of pocket must simply go without.

Such was the case with another one of Barrera's clients, a construction worker who suffered massive head injuries when he fell off a 25-foot-high roof, then had to wait nearly a year to get speech and cognitive therapy until a judge ruled in his favor.

Velazquez, the roofer who was paralyzed in the fall from a townhouse in February, was luckier in that regard. His employer was insured and did not contest Velazquez's claim that he slipped on a piece of tar sheeting that had not been properly nailed to the roof. He is now getting $373 a week in compensation benefits, plus medical care.

But that is small consolation for a man who once reveled in his speed on the soccer field. Still too fragile to return to his wife and children in the central Mexican city of Morelia, he has as yet been unable to persuade immigration authorities to allow relatives to come to him.

So he has had few visitors to lighten his mood as he soldiers through a succession of bedsores, excruciating nerve spasms and other complications of paralysis.

At first, Velazquez said, he spent the hours of isolation staring blankly through his nursing home window, sliding ever deeper into what seemed an unfathomable despair.

But in the past two months, he has begun to search for more active ways to pass the time.

Perhaps, he wonders, he can catch up on some of the schooling he missed when his father set him to work selling vegetables on the street at age 8. As a start, he's borrowed a book of Spanish love poems by Latin American authors. And he's even learning a little English from an instruction video.

On a recent afternoon, he rolled his wheelchair up to a nurse and tried out one of his newest phrases: "Medicine for pain, please?"

Mario Perez, injured in a construction accident, uses a work simulator at Rehabilitation Services of Greater Washington in Shady Grove.Velazquez eats lunch at the nursing home, using a strap to hold his fork. Workers' compensation covers his care.A puddle reflects Pedro Velazquez getting fresh air at the nursing home in Manassas where he has lived since a work accident left him paralyzed.An occupational therapist massages Perez's hand. A falling piece of plasterboard severed one of his tendons