The federal government is struggling to deal with an unusual increase in applications from immigrants who want to become American citizens, resulting in waits of at least 16 months that are threatening to prevent immigrants from voting in November’s presidential election.

New numbers released yesterday show a surge in citizenship applications last summer to be much more concentrated during the month of a fee hike by the federal government than previously thought.

The fees to apply for American citizenship rose to $675 from $400 starting July 30, 2007. In July 2007, applications jumped by more than 600% from the previous year. In that one month, 460,294 people applied to become citizens, according to numbers obtained from the federal government and released yesterday by the Migration Policy Institute, a pro-immigration think tank whose chairman is the Bishop of Brooklyn, Nicholas DiMarzio.

“It’s a really dramatic increase,” a senior fellow at the Migration Policy Institute, Doris Meissner, who was commissioner of the Immigration and Naturalization Service during the Clinton administration, said. “It’s the volume that is unusual.”

Some critics and immigration advocates have suggested the United States Customs and Immigration agency was unprepared for the large number of people who applied before the increase in fees went into effect. The long wait — now at least 16 months for applicants who filed to become naturalized citizens after June 2007, up from six months for those who applied before — is threatening to prevent many immigrants from voting after they had specifically applied in the hopes of participating in the presidential election. Legal permanent residents who applied after June 2007 have received letters advising them that they can expect to schedule their interview with immigration officials in about 500 days.

“I think in retrospect, you have to conclude that they did not do enough. They did not have their ear to the ground as fully as one would hope,” Ms. Meissner said.

“It was a perfect storm: the increase, the negative tone on immigration, and the fact that we were coming up on elections,” the Washington director of the National Association of Latino Elected and Appointed Officials, William Ramos, said.

Mr. Ramos said his organization met in January 2007 with officials from the U.S. Citizenship and Immigration Services, as the Immigration and Naturalization Service has been renamed, to inform them about a campaign they were preparing to launch ahead of the 2008 presidential elections called “Citizenship, It’s Time.” Mr. Ramos said his group suggested to federal officials at the time that they hire more staff to prepare for a likely surge in naturalization applications.

“We told them, look, this is what is going to happen,” Mr. Ramos said. “Now, they’re scrambling.”

The USCIS has said that it expected the surge, and has contended that the fee increase was necessary so that it could streamline its systems to process applications more efficiently and hire more agents. Officials say they are now in the process of hiring 3,000 new USCIS staff with the extra money earned from the fees, although the agency has also noted that training the new staff will take time, making it unlikely that wait times will drop anytime soon.

“We needed to increase the fees because we did need more people. But it’s not only to hire people, it’s to improve the resources,” a spokeswoman for the agency, Chris Rhatigan, said. “Our technology was a stubby pencil and paper.”

Except for the July 2007 surge, the numbers of people applying and being approved for citizenship have held relatively steady for the past eight years, according to numbers released yesterday by USCIS. In the two months after the fee increase went into effect, the numbers of applicants dropped off significantly from those months the previous year, with a 72% drop in the number of applicants in August and a 58% drop in September.

In December 2007, the last month for which data is available, 33,536 applied to become citizens and 62,956 applicants were approved. In December 1999, 28,413 applied and 65,794 were approved.

Many of the new applicants are Hispanic, a voting block that has been shifting back toward the Democrats after a period in which Republicans had been building up more Hispanic support.

USCIS has denied that its decision to implement the fee increase was politically motivated, and Ms. Meissner noted that the loss of potential votes from the new applicants would likely affect both Democrats and Republicans — especially with Senator McCain, who has supported a path to citizenship for illegal immigrants and has been praised by some immigrant advocates, as the Republican nominee.

Congress has begun to hold hearings on the backlog. Some have suggested that lawmakers could help alleviate the problem by changing the agency’s funding structure so that it doesn’t rely so heavily on fees.

Both the USCIS and its critics yesterday pointed out the positive side to the application surge: an increasing desire among the country’s growing immigrant population to integrate themselves into their new home.

“Our democracy is built on the notion of participation, so it is really a positive sign,” Ms. Meissner said.

Ms. Rhatigan echoed her: “Having this many people saying I want to be part of America, it’s good.”