WASHINGTON -- President Bush urged Congress on Saturday to find a middle ground between mass deportation or instant U.S. citizenship for the estimated 12 million illegal immigrants already living in America.

Bush's radio message was the third time this week he has spoken out about immigration.

On Monday, in a televised address from the Oval Office, Bush said he would order as many as 6,000 National Guard troops to secure the U.S. border with Mexico, and urged Congress to give millions of illegal immigrants a chance at citizenship.

Bush said the National Guard troops would fill in temporarily while the nation's Border Patrol is expanded. He asked Congress to add 6,000 more Border Patrol agents by the end of his presidency and add 6,700 more beds so illegal immigrants can be detained while waiting for hearings.

However, Homeland Security Department Inspector General Richard L. Skinner said in a report Friday that the administration hadn't budgeted enough, and that it will take nearly 35,000 more jail beds to detain all high-risk aliens.

Many congressional Republicans said they supported Bush's plan to use National Guard troops at the border. But he ran into criticism from some border state governors, Democrats and some other Republicans.

"This week I asked Congress to provide funding for dramatic improvements in manpower and technology at the border," Bush said Saturday. "We'll hire thousands more Border Patrol agents. And to help these agents do their jobs, we will deploy advanced technologies such as high-tech fences in urban areas, infrared cameras and unmanned aerial vehicles."

Many congressional Republicans said they supported Bush's plan to use National Guard troops at the border. But he ran into criticism from some border state governors, Democrats and some other Republicans.

Senate Democratic Leader Harry Reid said Bush must stand up to right-wing members of his own party who are working to block Senate action on an immigration bill.

Reid called on Bush to denounce the approach of House Republicans, who won passage of a tough immigration bill that would erect fences along the Mexican border and treat people who sneak across as felons to be deported.

On Thursday, the president traveled to Arizona to tour an unfortified section of the border in the desert. He endorsed using fences and other barriers to cut down on illegal crossings. The Senate on Wednesday voted to put 370 miles of fences on the border.

"To secure our border we must create a temporary worker program that provides foreign workers a legal and orderly way to enter our country for a limited period of time," Bush said. "

Bush wants an immigration bill that pairs up better security on the border with a guest worker program.

He faces opposition from conservative Republicans, particularly in the House, who prefer a get-tough approach and largely oppose a guest worker program -- something they view as giving amnesty to criminals. House legislation that passed last year would make all illegal immigrants subject to prosecution as felons.

The Senate, meanwhile, is working on broad legislation that largely answers Bush's call. It includes measures to tighten control of the borders, creates a guest worker program and offers a path to citizenship to many, but not all, illegal immigrants in the nation.

Sen. Jeff Sessions, R-Ala., an ardent opponent of the Senate bill, conceded Friday that the measure is likely to pass next week. "The Senate should be ashamed of itself," he said. But he also predicted that it won't become law unless House and Senate negotiators rewrite it.

In addition to a guest worker program, Bush said employers need to be held accountable for the workers they hire by creating a better system for verifying documents and work eligibility. The president said the system should include a tamperproof identification card for every legal foreign worker.

"The card would help us enforce the law and leave employers with no excuse for breaking it," he said. "And by making it harder for illegal immigrants to find work in our country, we would discourage people from crossing the border illegally in the first place."

That doesn't, however, resolve the status of millions of illegal immigrants already living in America. Bush said they should not be given an automatic path to citizenship.

"This is amnesty, and I oppose it," he said.

But the nation needs to provide a way for illegals to stay, he said.

"Illegal immigrants who have roots in our country and want to stay should have to pay a meaningful penalty, pay their taxes, learn English and work in a job for a number of years," Bush said.