Mexico City ? Would-be immigrants may be staying home in significant numbers, a Mexican government survey says, a trend that analysts on Tuesday attributed to a crackdown on illegal border crossers, raids at employment sites, and a slowing U.S. economy, particularly in the construction industry.

The third-quarter survey, used to determine the employment rate because many workers are off the tax rolls, showed a 30 percent drop in the number of people planning to work abroad or to cross the border from the third quarter of 2005.

About 76,000 Mexicans were “looking for a job in another country or preparing to cross the border,” according to the survey by the National Institute for Statistics and Geography, or INEGI for its initials in Spanish.

Two years earlier, that number was 107,500. INEGI pollsters use a formula to make those estimates based on the percentage of Mexicans age 14 and older who said they would seek work abroad. The survey’s overall margin of error is plus-or-minus 1.5 percent.