PHOENIX — When Alejandro Severino crossed illegally into the United States in 1999, there was no going back.
As security tightened on the U.S. side of the border -- new barriers were built and it was flooded with Border Patrol agents -- a return to central Mexico to visit his wife and child carried the risk that he might not be able to get back to his job in Phoenix.
It made the difficult decision to have his family join him here easier.
Studies show that because it is harder to crisscross the border, illegal immigrants who intended to be in the U.S. for limited stretches may increasingly be choosing to bring their families with them -- and settle permanently.
Today, Severino and his wife own an avocado-colored four-bedroom ranch house in a suburb, where their 9-year-old son, Diego, attends school. Fearing possible deportation, they agreed to be identified only by Alejandro's mother's last name. Their story is typical.
"A hundred people come from Mexico to the U.S., but only 20 go from the U.S. to Mexico," Severino said. "If you return, the border is more dangerous now than ever. How will you get back?"
Mexican government surveys show that 20% of illegal Mexican immigrants returned home after six months in 1992, compared with 7% in 2000.
"The net effect of the militarization of the border since 1993 has been to transform a circular movement of male workers to a settled population of families," said Douglas S. Massey, a Princeton University sociologist who has long studied the phenomenon. "Once they're here, they hunker down to stay longer."
Massey and other analysts argue that if Congress tightens border security again, more illegal immigrants will put down roots in the U.S.
"Every time we try to solve this problem, we end up shooting ourselves in the foot," said Dawn McClaren, an economist at Arizona State University in Tempe who studies immigration issues.
Advocates of greater border security acknowledge that it may cause some immigrants to stay permanently in the U.S. But they cite census data showing that for 30 years -- well before the border was tightened -- increasing numbers of people born in Mexico were settling in the United States.
Other factors, they contend, have been more important in pushing the number of illegal immigrants to more than 11 million.
"Maybe we would have had 10 million" if security didn't cause some illegal crossers to stay in the U.S., said Steve Camarota of the Center for Immigration Studies in Washington, which advocates tougher border enforcement. "But the run-up [in illegal immigrants] has more to do with a lack in border enforcement and a sense that America isn't serious about its laws."
Data on illegal immigrants are notoriously unreliable because most undocumented immigrants don't advertise their presence. But several academic studies show that they are staying longer, and suggest that the increased difficulty in crossing the border is a factor.
The probability of returning home started to dip after President Reagan in 1986 signed an amnesty law for illegal immigrants, according to data compiled by Massey and Mexican researchers. It dropped again after 1993, when the U.S. government began fortifying the border in El Paso and San Diego, the two most popular points for illegal entry.
The fortification pushed crossers into the unforgiving deserts of the Southwest. The cost of a coyote, or human smuggler, to bring people into the U.S. has risen from $143 in 1993 to more than $2,000 today. Deaths during crossings soared to a record 460 last year.
Meanwhile, the number of Mexican-born residents living in the U.S. jumped sharply after the border buildup began, census data show.
Felix Lopez's experience shows why. The Phoenix construction worker easily entered the United States illegally in 1995, and didn't go back to Mexico until his mother died last year. After a harrowing three-day crossing through the Arizona desert -- during which he said he heard voices of people who had died on earlier treks -- he vowed never to return to Mexico. "I'm not doing it again," Lopez said of the journey.
The difficulty deters some immigrants from sending for their families.
Luis, an Ecuadorean who did not give his last name because he feared being deported, dashed across the San Diego County border in 1999. He said in an interview that he had told his six children not to join him -- even though they could make far more money in Phoenix than in their mountain town in Ecuador. "It's too difficult getting in here now," he said.
But many still make the journey. In Mexico, entire villages have emptied out as women and children have gone to join husbands and fathers in the United States. Wayne A. Cornelius, director of the Center for Comparative Immigration Studies at UC San Diego, surveyed villages in Jalisco state in 1995 and again last year. In the first survey, one village had 36 houses abandoned by families moving north; last year the number had grown to 138.