WASHINGTON — The Bush administration has sharply ratcheted up prosecutions of illegal immigrants along the U.S.-Mexico border in the last year, with increases so dramatic that immigration offenses now account for as much as half the nation's federal criminal caseload.
In the widening crackdown, administration officials prosecuted 9,350 illegal immigrants on federal criminal charges in March, up from 3,746 a year ago and an all-time high, according to statistics released Tuesday. Those convicted have received jail sentences averaging about one month.
The prosecutions are among the most visible steps in a larger effort that includes work-site raids, increased border patrols and the use of technology and fences. Often controversial, the patchwork of measures represents the administration's response to failed congressional attempts last summer to overhaul federal immigration laws.
Administration officials and conservative groups have lauded the increase in prosecutions. But critics say data show illegal immigrants are still trying to enter the country. And some lawyers argue that the push is overwhelming a federal court system with limited resources and higher priorities.
Even so, administration officials announced this month that they would be funneling more resources toward the effort, called Operation Streamline.
"The results of this criminal prosecution initiative have been striking," said Homeland Security Secretary Michael Chertoff.
Chertoff's agency and the Justice Department, which oversee the effort, recently announced a plan to assign 64 attorneys and 35 staff members to prosecutions along the Southwest border.
The program began as a pilot around Del Rio, Texas, in 2005 and spread to other areas. Officers and prosecutors participating in it practice "zero tolerance," and jail times can range from two weeks to six months.
"The reason this works is because these illegal migrants come to realize that violating the law will not simply send them back to try over again but will require them to actually serve some short period of time in a jail or prison setting, and will brand them as having been violators of the law," Chertoff said. "That has a very significant deterrent impact."
The statistical analysis released Tuesday was compiled by Syracuse University's Transactional Records Access Clearinghouse, considered an authoritative source for such figures. It called the increase "highly unusual."
Operation Streamline's larger aim is to give the administration another tool to use in its crackdown on illegal immigration, said Susan B. Long, a TRAC co-director and Syracuse University professor.
"This is an effort to use the federal criminal justice system in immigration enforcement," Long said. "What it means is that immigration cases are dominating the federal court system these days. The volume of cases is really huge. This is a big deal."
Of 16,298 federal criminal prosecutions recorded nationwide in March, immigration cases accounted for more than half, Long said. The next-highest number, 2,674, was for drug offenses, followed by 702 for white-collar crime.
TRAC researchers found that all but 142 of the 9,350 new federal immigration prosecutions in March occurred in certain areas along the border with Mexico. Texas was most active, followed by Southern California.
California is not formally a part of the program. But prosecutions of people who smuggle illegal immigrants across the state's border have increased sharply in the last five years, nearly doubling to 118 cases in March.
The deluge of prosecutions is overwhelming some lawyers involved in the process.
Heather Williams, a federal public defender in Tucson, said the operation had a crushing effect when it was begun this year on a limited basis.
Defense attorneys fear for clients who are hustled into court, en masse, after spending days crossing the desert.
"We have to be concerned our clients are competent to plead, that they understand what's going on," Williams said.
Other immigrant advocates were critical of the increase in federal prosecutions.
"It doesn't mean we have an end to illegal immigration or a way of dealing with it," said Angela Kelley, director of the Immigration Policy Center.
A recent study showed that would-be border crossers were more concerned about heat and harsh conditions than border enforcement, she said. The study, by Wayne A. Cornelius, director of the Center for Comparative Immigration Studies at UC San Diego, found that 98% of immigrants from the Mexican state of Oaxaca were eventually able to enter the U.S.
But groups that want to see immigration tightly controlled applauded the new statistics.
"It sounds like very good news," said Roy Beck, director of NumbersUSA, which advocates stricter immigration controls.
"It's part of a pattern we've seen since last August where the administration, on the border and in the interior, seems almost monthly to be tightening the vise," he said.
Times staff writers Richard Marosi in San Diego and Nicholas Riccardi in Denver contributed to this report.