MEXICO CITY - Lorenzo Martinez, an illegal immigrant who has lived in Los Angeles for six years, has a message for his kin in Mexico's Hidalgo state: Stay put.

The steady construction work that had allowed him to send home as much as $1,000 a month in recent years had disappeared. The 36-year-old father of four said desperation was growing among the day laborers with whom he was competing for odd jobs.

Sporadic employment isn't the half of it. Martinez said anxiety also was running high among undocumented workers about stepped-up workplace raids, deportations, and increasing demands by U.S. employers for proof that they were in the country legally.

"Better not to come," Martinez said. "The situation is really bad."

That message seems to be getting through. There are numerous signs of a slowdown in illegal immigration:

A recent survey by Mexican authorities shows that fewer Mexicans say they plan to seek work outside the country. In the third quarter of 2007, about 47,000 said they would be packing their bags, down nearly a third from the same quarter a year earlier.

U.S. border authorities arrested just under 877,000 illegal crossers in fiscal 2007, which ended Sept. 30, down 20 percent compared with the year before. A drop in apprehensions is often interpreted as a sign that fewer migrants are attempting the trip.

The growth rate of the U.S. Mexican-born population has dropped by nearly half, to 4.2 percent in 2007 from about 8 percent in 2005 and 2006, an analysis of census data by the Pew Hispanic Center found.

Employment of foreign-born Hispanics increased at a slower pace in the first quarter of 2007 than in the same period in the previous three years, according to Pew. The slowdown was particularly noticeable in the construction industry. Growth in employment of foreign-born Hispanics in that sector was 10.9 percent early this year, compared with an average first-quarter growth rate of 19.8 percent from 2004 to 2006.

The growth in remittances sent to Mexico has dwindled to a trickle. Through October, Mexicans living abroad sent $20.4 billion home to their families, a 1.3 percent increase over the 2006 period, according to Mexico's central bank. Those sums were growing more than 20 percent annually just a few years ago.

What is behind the apparent decline?

Some say it's primarily the slump in U.S. construction, which has been a magnet for undocumented workers over the last few years - one in five Hispanic immigrants works in the building trades. Others say the drop is largely a result of stepped-up enforcement.

Proponents of tighter security say U.S. workplace dragnets and increased deportations have made big headlines in Latin America, deterring some would-be migrants.

U.S. authorities are installing hundreds of miles of fencing along the southern border. About 15,000 Border Patrol agents have been deployed to the region, 25 percent more than in 2006. By the end of 2008, 3,000 more are slated to be in place.

"It's a combination of personnel, technology and infrastructure," Ramon Rivera, a spokesman for Customs and Border Protection, said.

Immigration experts say tougher enforcement is one of several explanations. The border buildup has encouraged more illegal immigrants to employ professional smugglers, whose success rate is higher than that of individuals, said Wayne Cornelius, director of the Center for Comparative Immigration Studies at the University of California, San Diego.

He said tougher enforcement had also discouraged many undocumented workers from returning to their homelands for occasional visits, for fear of getting caught reentering the United States. Fewer people crossing the border means fewer apprehensions.

The fall in arrests also fits a familiar pattern, one that traditionally has more to do with the strength of the U.S. job market than with walls or guards.

"It's the economy, stupid," Cornelius said.

Demographer Jeffrey Passel said the U.S. unemployment rate was the strongest correlating factor he had found in tracking migratory flows. In November, the jobless rate for Hispanics was 5.7 percent, up from 5 percent in November 2006.

"When it's easy to get a job, they come. When it's hard to get a job, they don't," said Passel, senior research associate at the Washington-based Pew Hispanic Center.

Border authorities apprehended a record 1.7 million would-be migrants in 2000, at the height of the technology boom. That number tumbled over the next three years amid a U.S. recession, the Sept. 11 attacks, and the loss of more than two million jobs. About 932,000 illegal crossers were apprehended in 2003, a drop of more than 44 percent from 2000, according to Customs and Border Protection.

At the time, some credited the decline to tightened border security after Sept. 11. But arrests rebounded strongly in 2004 and 2005 as foreign-born workers flocked to the United States to fill jobs in the building trades.

As the bust in the U.S. housing market eliminates construction jobs, Mexico's economy is proving resilient, giving Mexicans added incentive to stay home. Job creation has been solid over the last two years, with nearly two million positions added in the formal economy.

Although most jobs in Mexico pay a fraction of what they would in the United States, some Mexicans may be deciding that poorly paid work is better than none, given the uncertainty over the border.