This year a smaller percentage of Mexican immigrants in the United States sent money back to their homeland than in 2006, according to a report released yesterday by the Inter-American Development Bank. The bank said the reduction had left at least two million people in Mexico without the same financial help they had once received.

Bank officials, pointing to a survey of Mexican immigrants in the report, said the decline reflected a rising sense of insecurity and uncertainty about whether they would stay in the United States. Anticipating a possible move back to Mexico, these immigrants appear to be saving more.

“They have decided because of the uncertainty of the future that they need to step back and save a bit,” said Donald F. Terry, general manager of the Multilateral Investment Fund at the bank.

Mr. Terry said the slowdown would affect about 500,000 Mexican homes. “For those families in Mexico, there is going to be economic and social dislocation,” he said.

Over all, the percentage of Mexicans who regularly sent money home fell to 64 percent in the first half of this year, compared with 71 percent for all of last year, according to the report. The sharpest decline in such transactions — known as remittances — came among Mexicans living in states where they have settled in large numbers only recently, like Georgia, North Carolina and Pennsylvania. In those states, the percentage of Mexicans sending money home fell to 56 percent from January to June, from 80 percent in 2006.

In the survey, only 49 percent of the Mexicans living in states with relatively recent immigration said they expected to be living in the United States five years from now. Sergio Bendixen, a Miami pollster who conducted the survey, said the percentage of Mexicans considering a return to their country was the highest in the more than two decades he has interviewed Hispanic immigrants.

The immigrants in the survey included American citizens and legal and illegal residents. They identified discrimination as the biggest problem they faced, with 83 percent saying that discrimination against Latin American immigrants in general was growing in the United States.

“Mexican immigrants don’t feel welcome in the U.S. anymore,” Mr. Bendixen said. “They feel they are not wanted here, and their contributions are not appreciated.”

Until this year, money sent home by Mexicans working in the United States had shown spectacular annual growth since 2000, the first year it was systematically recorded by Mexico’s central bank. Last year, these funds totaled $23 billion, making them the country’s second-largest source of foreign income after oil.

But in the first half of 2007, there was no significant increase over the $11.4 billion sent to Mexico in the first half of 2006, a period that recorded a 23 percent increase over the same months in 2005.

By contrast, the amount of money sent home by immigrants from Central America has continued to grow, according to the development bank.

Remittances to Mexico have become vital to the economics of the country’s poorest regions, bank officials said. The money pays for drinking-water systems, roads, care for older people and other needs in villages and working-class neighborhoods.