President Bush urged lawmakers on Saturday to come together on the complex and emotional issue of immigration, calling it "a critical challenge" now before the nation.

"We need a system where our laws are respected. We need a system that meets the legitimate needs of our economy. And we need a system that treats people with dignity and helps newcomers assimilate into our society," he said in his weekly radio address. "We must address all elements of this problem together, or none of them will be solved at all."

There are an estimated 12 million illegal immigrants in the country, and passions run high on what to do about them. Bush wants to establish a temporary worker program for some of them and create a path to citizenship — albeit a difficult one — for many. He says it is unrealistic to propose that millions of people be deported.

What he likes to call comprehensive immigration reform was once Bush's top domestic priority.

But the president was stymied by members of his own party, who controlled Congress until January. While business and industry are demanding more low-wage workers, many conservatives reject the president's approach as putting the interests of illegal immigrants before those of American workers.

The Senate passed a plan last May that would allow illegal immigrants a chance at citizenship and create a temporary guest worker program for new arrivals. But the proposal died in the House, where tough new border security measures were the priority.

Last October, Bush signed a get-tough bill that authorized 700 additional miles of fencing along the U.S.-Mexico border.

Since then, the White House has been emphasizing that new efforts along the border are having an impact, while quietly looking for bipartisan compromise on broader legislation. Bush says he is determined to enact something — and it is one the few issues on which he might be able to claim victory with Congress in Democratic hands.

He gave that effort a renewed push by devoting his radio address to the topic, and making it the subject as well of a commencement speech he was giving Saturday afternoon at Miami Dade College in Florida.

Bush said the talks are bearing fruit, persuading some who had doubts about comprehensive reform to now be open to it.

"I know convictions run deep on the matter of immigration. Yet I am confident we can have a serious, civil and conclusive debate," the president said. "Our nation deserves an immigration system that secures our borders and honors our proud history as a nation of immigrants."

One approach that grew out of the initial talks between the White House and Capitol Hill would still give illegal immigrants a path to citizenship, although it would be much tougher than a Senate-approved measure. The new approach would require fines, trips back home, long waits and hefty penalties. Conservatives still called it overly permissive, essentially amnesty for illegal behavior.

Most national polls show Americans are overwhelmingly supportive of an immigration overhaul that would allow those here illegally to stay, work and earn their way to legal status.