(Updates with more detail)
By Andy Sullivan
WASHINGTON, Jan 15 (Reuters) - U.S. Homeland Security Secretary-designate Janet Napolitano promised at her confirmation hearing on Thursday to step up pressure on companies that hire illegal immigrants, and key senators said they would move to approve her nomination swiftly.
"You have to deal with illegal immigration from the demand side, as well as the supply side" by working with the Justice Department to prosecute companies that hire illegal workers, the Arizona governor said.
Napolitano, 51, was roundly praised by members of the Senate Homeland Security and Governmental Affairs Committee, who said they would move to confirm her as soon as possible after Democratic President-elect Barack Obama takes office on Jan. 20.
"You have shown yourself ready to take on the awesome responsibility that comes with being the secretary of Homeland Security," said committee chairman Joe Lieberman, a Connecticut independent.
If confirmed, Napolitano would oversee a sprawling agency of 200,000 employees responsible for securing the country's borders, screening airline passengers, responding to natural disasters and protecting chemical plants and other infrastructure against terrorist attacks.
Cobbled together from 22 separate agencies after the Sept. 11 attacks in 2001, the department has faced widespread criticism for its disorganized response to Hurricane Katrina in 2005 and its sometimes-haphazard airline security measures.
The agency has also struggled to stem the flow of illegal immigrants and drugs, most recently through surveillance technology and a controversial barrier fence along one-third of the 2,000-mile (3,200-km) U.S.-Mexico border.
Napolitano, who as governor pressed the U.S. government to reimburse her state for enforcing immigration laws, said she would install more effective sensors to supplement thinly stretched border guards.
But she seemed less than enthusiastic about the border fence, which has drawn opposition from property owners and environmentalists.
"There is a role for some fencing, particularly around urban areas ... but these borders are so vast that the notion that a fence alone is worth the expense to go from San Diego to Brownsville (Texas), I don't think that would be giving good advice to the committee," she said.
There are an estimated 12 million illegal immigrants living and working in the United States, and the issue has long been divisive.
Members of the committee praised Napolitano's experience as a U.S. attorney, state attorney general and governor and said she was ready to take the job. They said Congress should better coordinate oversight so agency officials spend less time testifying in front of different committees.
"There's no question you have the management qualifications," Ohio Republican Sen. George Voinovich said. "I'm impressed with the grasp you have of the department."
Napolitano said her first priorities would be to fill key positions and instill a collective sense of identity in the still-fractured agency, which only in recent weeks has found a site for a central headquarters.
(Editing by Cynthia Osterman and Frances Kerry)