The number of immigrants applying to become U.S. citizens plunged 62 percent last year as the cost of naturalization rose and the economy soured, according to an analysis released Friday by the National Council of La Raza, a Latino advocacy organization.

In late 2007, the application cost increased from $330 to $595, plus an $80 fee for computerized fingerprinting. Partly in anticipation of the price increase, 1.38 million people filed applications in 2007, creating a backlog that nearly tripled the average processing time.

Last year, the number of applicants fell to 525,786, the smallest since 2003. The largest was 1.41 million, in 1997, just before a 76 percent fee increase.

Citing a decline in real median income among non-citizens in recent years, the analysis said that "eligible applicants face mounting economic pressures that threaten to place naturalization out of reach." It recommended seeking ways for the government to help defray the cost of processing applications, which depends on fees, and suggested freezing fees at their levels now.

Doris Meissner, a senior fellow at the Migration Policy Institute, a Washington-based think tank, and former commissioner of the Immigration and Naturalization Service, said a rise and fall in applications is typical when a fee increase is imposed. In this case, the increase was greater than usual because it paid for technological upgrades and improved security checks, she said.

But she added that the 2007 spike in applications was also a response to concentrated efforts by immigrant groups to increase the number of voters before last year's elections.

According to a March Homeland Security Department report, natives of Mexico account for the largest group of immigrants naturalized each year, and the largest number of applicants live in California, Florida and New York.

But last year, the Washington area, along with Miami-Fort Lauderdale, saw the biggest increase in naturalizations. In 2008, 40,729 residents of the Washington region became citizens, compared with 19,364 the year before. Most had applied before the rate increase. The largest groups to apply were natives of El Salvador and India.

Eliseo Medina, executive vice president of the Service Employees International Union, whose membership includes large numbers of immigrants, said the government should do more to ease the way for would-be citizens through fee defrayment, information workshops and English classes. "The nonprofit sectors -- churches, community organizations and unions -- have stepped in, but it shouldn't be just put on their back," he said.

Meissner said she agreed with the report's call for new revenue models but doubts the fee increase will deter many citizenship-seekers. "Citizenship is a very, very valuable commodity," she said. "People do what they can to become citizens, and they will make every effort, including saving up the money that's needed."