By GINGER THOMPSON

MEXICO CITY, Oct. 27 — Nearly one Mexican in five regularly gets money from relatives employed in the United States, making this country the largest repository of such remittances in the world, according to a poll sponsored by the Inter-American Development Bank.

The pollster, Sergio Bendixen, estimates that the payments helped feed, house and educate at least a quarter of Mexico's 100 million people.

The poll was part of a report on Monday by the bank, which said money sent home by Mexican emigrants will soar to $14.5 billion this year, exceeding tourism and direct foreign investment to become this country's second most important source of income. Oil remains No. 1.

Mr. Bendixen said the poll offered forceful evidence that remittances not only sustained the rural poor but have also become important to urban working-class households.

Roberto Suro, director of the Pew Hispanic Center, estimated that annual remittances to Mexico and Central America could reach $25 billion by the end of the decade, a vast sum made of countless tiny payments by America's lowest-paid workers.

"This is not necessarily something to celebrate," said Don Terry, manager of the Multilateral Investment Fund. "It means that the Mexican economy is not expanding and so people have had to leave."

Indeed, in addition to showing a significant jump in remittances, the report opened a window onto the shifts in illegal immigration to the United States since the terrorist attacks on Sept. 11, 2001.

In the wake of the attacks, the United States almost immediately dispatched more people and machinery to bolster law enforcement operations on its border with Mexico, and it was believed that the heightened security would discourage immigrants from their illegal crossings.

With fewer immigrants heading north, experts on both sides of the border predicted, remittances to Latin America would sharply decline. And the shrinking American economy was expected to force immigrants out of work, leaving them less money to send to relatives back home.

Those forecasts, according to the Inter-American Development Bank and immigration experts, have proved wrong.

Despite the increased risks of crossing the border, United States population estimates show that the northward flow continued to surge, and experts said the immigrant laborers had proved themselves resistant to a stormy economic climate.

Mexican immigration experts, including Rodolfo García Zamora of the Autonomous University of Zacatecas, estimated that some 450,000 Mexicans entered the United States illegally last year. Mr. Suro said other evidence indicated that the American population grew last year by nearly one million people from Latin America. More than half, he estimated, had no legal status.

"For most Mexicans, the increased risks of crossing the border have had no impact on their willingness to migrate," Mr. Suro said. He recalled a focus group interview in which he asked a conference room full of Mexican men and women how many of them were considering migrating to the United States. They all raised their hands, he said.

The $14.5 billion in remittances reported by the bank marked a significant increase over the estimated $9 billion that emigrants reportedly sent home three years ago. The Mexican government estimated that remittances this year would reach $12 billion, but authorities at the bank said they had adjusted their figures to include money that had come into Mexico through informal channels.

Most of the money is spent on food, clothing and housing. But Mr. Suro said a growing portion was invested in small business or helped to pay for high school and college educations.

Across much of central Mexico, where men and women have migrated to the United States for so many decades that crossing the border has become more a rite of passage than an escape from poverty, remittances exceed state public works budgets and pay to build roads, schools, water systems and baseball stadiums.

In recent years the United States and Mexico carried out reforms aimed at making it easier and more affordable for migrants to transfer money home. Companies like Western Union cut the fees they charged for wire transfers, halving the cost of transferring money, and American banks have begun allowing illegal immigrants to open accounts so relatives at home can withdraw funds from automatic teller machines.

Those changes have begun to ease the negative attitudes that Mexicans have long held toward financial institutions. Some 45 percent of people polled by the bank said they received their remittances from a bank or other credit institution, compared with only 7 percent in Guatemala and 17 percent in Ecuador.

The opening of more formal channels has made it easier to measure the cash flow, Mr. Terry said. And he said at least a part of the significant jump in remittances could be attributed to better accounting.

The figures have been the focus of an emerging debate among Mexican experts. At a conference last weekend in Zacatecas, several charged that the Mexican government had inflated remittance figures to help brighten an otherwise dreary economic report.