A tough new Arizona law aimed at rooting out illegal immigrants is reshaping the arguments used by the Obama administration and congressional Democrats in support of a sweeping overhaul of the nation's immigration system.

White House officials say the Arizona law underscores an untenable void in federal immigration policy. Without congressional action, they warn, Arizona and other states will create a patchwork of laws that don't resolve the core problem: how to strengthen the borders and deal with the 11 million people who are in the U.S. illegally.

"The president has said ... that this is a wake-up call for the federal government to act," said White House Press Secretary Robert Gibbs.

It was unclear Monday whether that argument will prove to be the catalyst in overcoming the thorny politics surrounding immigration. But the Arizona law is now part of the message that proponents of a federal overhaul are deploying to pass a bill with bipartisan support.

"There's a substantive and moral sense of urgency around this now because of the potential consequences of this [Arizona] legislation," said Janet Murguia, president of the National Council of La Raza, a Latino civil rights group.

Obama's game plan is not to put forward his own bill, but rather to wait for a pair of influential senators, Lindsey Graham (R-S.C.) and Charles E. Schumer (D-N.Y.), to release a proposal that might command bipartisan backing.

The two have spent months crafting a blueprint. But Graham in recent weeks has insisted publicly that the White House must come forward with its own plan.

However, Graham did not make that request when he met privately with Obama at the White House last month to strategize about immigration, according to people familiar with the meeting. Instead, he asked Obama to help round up potential Republican votes, they said.

Complicating matters for the White House is a divided Democratic caucus. Two Democratic senators, Ben Nelson of Nebraska and Blanche Lincoln of Arkansas, privately have told Democratic leaders they would prefer to see immigration delayed until 2011, according to a Democratic Senate aide.

That means the White House would have to round up more than token Republican support if an immigration bill is to have a chance of passing this year.

The Arizona law has emerged as a wildcard in the national debate.

Last week, Arizona Gov. Jan Brewer signed a measure that empowers local authorities to prosecute people in the country illegally. Described as the toughest anti-immigration law in the U.S., it has spawned fears that police will target minorities on the thinnest of suspicions.

Joining the critics is Mexican President Felipe Calderon. On Monday, Calderon said the Arizona law "opens the door to intolerance, to hatred, to discrimination and to abuse." He vowed to use "all resources available" to defend Mexicans who run afoul of the law.

Speaking on the Senate floor, Sen. John McCain (R-Ariz.) defended the law. At one time, McCain was a voice for broad-based immigration changes. Now, challenged in his Senate reelection bid by a conservative primary opponent, McCain is taking a hard-line stance on immigration, focusing more on border security than on finding a path to legal status for undocumented immigrants.

"There is no intention whatsoever to violate anyone's civil rights, but this is a national security issue," McCain said. "This is a national security issue where the United States of America has an unsecured border between Arizona and Mexico, which has led to violence [that is] the worst I have ever seen."

For Obama and his Democratic allies, time is short for passing a national immigration bill. Senators have only a few months to act before a new Supreme Court nomination and mid-term elections consume their time.

Other tough bills are competing for the attention of Congress, including a measure to curb global warming.

Senate Minority Leader Mitch McConnell (R-Ky.) believes that steps to alleviate unemployment should take precedence over immigration legislation this year.

"It strikes me that with all the border security problems we have down there ... and with 10% unemployment, it's not a great time to take this issue up in Washington," he said on Fox News.