A new Obama administration initiative that could allow thousands of young immigrants to avoid deportation and find work is fully within the president's legal powers, a top White House aide said Sunday.

Since the administration unveiled the measure on Friday, Republicans have already charged that Obama is illegally circumventing Congress and unilaterally changing immigration law. Rep. Steve King, R-Iowa, a vocal critic of illegal immigration, has said he will sue the president.

Senior Obama adviser David Plouffe rejected those charges on ABC's This Week, saying the administration is absolutely confident this is within our authority and defending the move as a short-term solution rather than a substitute for the kind of comprehensive legislation that would need to come from Congress.

The new policy does parallel the intent of a stalled piece of legislation, the DREAM Act, that would offer citizenship to undocumented immigrants who were brought to the country as children, have clean criminal records and have pursued college or military service. When the president articulated the iniative on Friday, he used language that closely tracked the arguments DREAM Act supporters invoke.

Now, these are young people who study in our schools, they play in our neighborhoods, they're friends with our kids, they pledge allegiance to our flag. They are Americans in their heart, in their minds, in every single way but one: on paper, Obama said, adding that the need to address that population is what gave rise to the DREAM Act.

But unlike with the DREAM Act, immigrants offered relief under the new policy would not be eligible for citizenship. They would be shielded from deportation and would be allowed to apply for work permits. They would also need to apply every two years to renew their immunity from deportation.

This is not a permanent fix, Plouffe said on This Week, adding that we need Congress to act here.

Central to the new policy is the concept of prosecutorial discretion, or the premise that immigration enforcement agents can decide which deportation cases to pursue or suspend. Because immigration enforcement is a federal responsibility, the Obama administration argues that it has the ability to dictate how Immigration and Customs Enforcement personnel exercise their discretion.

The same theory underlies a sweeping directive, issued last summer, that sought to realign immigration enforcement by having field agents and prosecutors focus on immigrants who posed a threat to public safety, had criminal records or had repeatedly broken immigration laws. Immigrants who had not committed crimes, had served in the military or had deep family ties were eligible under the new guidelines to have pending deportation cases suspended, although the process has so far produced scant results.

Likely Republican nominee Mitt Romney criticized the administration's shift on Friday, saying Obama was seeking a short-term solution for political gain. Latinos overwhelmingly supported Obama in 2008, and while polls still show the president soundly defeating Romney amongst Hispanics, many immigrant advocates have grown frustrated as deportations have soared to record highs under the Obama administration.

It's unfortunate that this sort of thing comes up four and a half months before the election, Romney said, adding that Obama did nothing to address immigration when Democrats controlled both houses of Congress.

Romney did sound a sympathetic note, a marked contrast from a Republican primary in which he embraced a hardline immigration stance, vowing to veto the DREAM Act and charactering his favored immigration policy as self-deportation.

I believe the status of young people who come here through no fault of their own is an important matter to be considered and should be solved on a long-term basis so they know what their future would be in this country, Romney said.