By Tabassum Zakaria and Deborah Charles
WASHINGTON (Reuters) - U.S. Homeland Security Secretary Janet Napolitano, a vocal supporter of immigration reform who became a target for Republicans, said on Friday she will leave her position to lead the University of California.
It was not clear who would replace her at the helm of the Department of Homeland Security, the third-largest U.S. department with a broad mandate including immigration and disaster response. She plans to leave in early September.
The former Arizona governor has been a proponent of immigration reform and her announcement came as the U.S. Congress grappled with an overhaul of immigration laws.
She also had a prominent role in briefing Congress and the public about terrorism.
An original member of President Barack Obama's Cabinet, Napolitano was praised for restoring the Federal Emergency Management Agency to good standing after its disastrous response to Hurricane Katrina in 2005 during the George W. Bush administration.
Obama thanked Napolitano for working "around the clock" to respond to natural disasters including the 2011 Joplin, Missouri, tornado and Hurricane Sandy that battered the Northeast last year, as well as other challenges.
"Since day one, Janet has led my administration's effort to secure our borders, deploying a historic number of resources, while also taking steps to make our immigration system fairer and more consistent with our values," Obama said in a statement.
"The American people are safer and more secure thanks to Janet's leadership," he said.
Republicans accused Napolitano of presenting an overly rosy picture of the administration's record on securing the U.S. borders. Other critics said she failed to solve problems in her sprawling department, which was voted the least satisfying government agency in which to work.
"The many agencies housed within DHS are only as effective as their leadership, and it is crucial that the administration appoints someone who does not underestimate the threats against us, and who is committed to enforcing the law and creating a unified Department," said Republican Michael McCaul of Texas, chairman of the House of Representatives Homeland Security Committee.
The Department of Homeland Security was created in response to the September 11, 2001, attacks. It combined 22 different departments and has more than 240,000 employees focusing on sectors including aviation, border security and cyber-security.
Some Democrats praised Napolitano for helping to reduce illegal immigration and for supporting a measure last year to relax deportation rules for young people brought to the United States without legal status.
"She did the right thing in exercising her authority to provide temporary relief against deportation for children who were brought to this country through no fault of their own," said Senate Judiciary Committee Chairman Patrick Leahy, a Vermont Democrat.
Some liberal Democrats and immigration rights groups, which had criticized Napolitano for the sharp increase in deportations during the Obama administration, said they welcomed a change.
"We hope the new head of the Department of Homeland Security restores some much needed discretion and accountability to a deportation machine that has already wreaked havoc on immigrant families and communities across the country," said Marielena Hincapie, director of the National Immigration Law Center.
The number of annual deportations jumped by about 27,000 from 2008 to 2011. It dropped slightly in fiscal 2012 from 2011 to a total of 366,292.
Democratic Senator Charles Schumer of New York wasted no time suggesting a replacement for Napolitano, urging Obama to appoint New York Police Department Commissioner Ray Kelly.
Marshall Fitz, an immigration specialist at the liberal Center for American Progress, said the selection of someone like Kelly who has a strong law-and-order reputation could help neutralize arguments from conservatives who have opposed comprehensive immigration reform legislation.
"If you were to insert into the process at this juncture a new chief enforcer along the lines of a Ray Kelly ... Republicans would have a tough time making the argument that the administration is not serious about border enforcement," Fitz said.
Another possible replacement could be FEMA administrator Craig Fugate, who has been praised for turning the agency around after Katrina and for presenting a calm public face during disasters.
Napolitano thanked Obama for the chance to serve the United States "during this important chapter of our history" and said she was looking forward to her new role focusing on "educating our nation's next generation of leaders."
The University of California system consists of 10 campuses plus five medical centers and three affiliated national laboratories. The UC system includes more than 234,000 students, with an operating budget of more than $24 billion.
Napolitano would be the first woman to run the UC system. Public education in California has been under growing pressure from state budget constraints aggravated by the state's prolonged economic slump.
(Additional reporting by Steve Holland and Richard Cowan in Washington and Steve Gorman in Los Angeles; Writing by Laura MacInnis and Deborah Charles; Editing by Doina Chiacu, Vicki Allen and Mohammad Zargham)