U.S. President George W. Bush on Monday tried to balance differences in his own Republican Party over illegal immigration by rejecting amnesty and calling for a hardened Mexico border but also vowing the United States would remain "a welcoming society."

Fueled by fears of terrorists slipping into the country, escalating violence and drug smuggling, Americans have become increasingly worried about illegal immigration. More than three-quarters think the government is not doing enough to control the borders, according to a CBS News poll last month.

At Davis-Monthan Air Force Base in Tucson, Bush portrayed his proposed temporary worker program -- which many Republicans say rewards lawbreakers and provides "backdoor amnesty" -- as a way to relieve pressure on enforcement by bringing illegal immigrants "out of the shadows."

Bush said the program would not create an automatic path to citizenship, but the United States had always been "a compassionate nation that values the newcomer" and "the American people should not have to choose between a welcoming society and a legal society."

On enforcement, he pledged to harden the border with increased manpower and new technology including unmanned aerial surveillance. He proposed returning illegals to hometowns in Mexico's interior and adding capacity to detention facilities.

The issue is expected to play a major role in congressional elections in many states next year.

His guest worker proposal offers the estimated 11 million illegal immigrants in the United States the chance to register and work -- mostly at low-skilled jobs Americans don't want -- for up to six years. They must then return to their home countries for a year to apply for a new work permit.