WASHINGTON — If the U.S. Supreme Court endorses a key immigration initiative of President Obama protecting more than 4 million illegal immigrants from deportation, his administration could face a surge of applicants and little time to process them before he leaves office in January 2017.

Obama announced the action in November 2014, but it has never gone into effect, being put on hold by a federal judge in Texas in February. The plan was designed to help illegal immigrant parents of children who are U.S. citizens or lawful permanent residents. It would protect them from deportation and give them work authorization.

The Supreme Court said it would decide whether Obama acted lawfully in creating the program by executive order, bypassing a gridlocked Congress. If Obama wins when the court rules by the end of June, his administration would have just seven months to implement the program.

Obama’s victory could be short-lived because the next president, to be elected in November, would have the final say on whether to keep the program in place.

Democrats, including presidential front-runner Hillary Clinton have embraced Obama’s plan. Republican presidential candidates including businessman Donald Trump and Texas Senator Ted Cruz have assailed it. Cruz said on Tuesday if elected he would rescind Obama’s order on the first day of his presidency.

An earlier immigration program that gave similar relief to children of illegal immigrants who grew up in the United States showed that such policies take time to implement. Launched in June 2012, it took two months to put in place.

After that, there were almost 408,000 applications in the first six months of the program, according to government numbers. By January 2013, only 154,000 applications had been approved. More than 700,000 people have since benefited from the program.

The government has been able to do nothing to prepare while Obama’s executive action has been on hold. In the injunction that halted the plan, U.S. District Judge Andrew Hanen specifically said the administration was barred from “implementing any and all aspects or phases” of the program.

A Department of Homeland Security spokeswoman said the federal government is complying with the injunction.

Immigration advocates said they are preparing for a new effort to educate potential applicants about the program. They forecast much higher numbers than those who applied to the earlier 2012 program, largely because many more are eligible.

“There is no way the administration can process the projected volume of people that would be eligible,” said Gregory Chen, director of advocacy for the American Immigration Lawyers Association.

The new program is likely to present additional bureaucratic problems, legal experts say, in part due to the larger pool of eligible people, but also because of the specific nature of the applicants. Both programs require proof of continued residency in the United States.

For younger people, this is easier to prove as usually they can cite school records, immigration experts say. For older people, who often do not speak English, it can be harder to provide necessary documentation. Women who do not work could find it especially difficult.

“It’s going to be a little bit more tricky for some applicants,” said Adonia Simpson, managing attorney for the Esperanza Center, an immigrant resource center run by Catholic Charities in Baltimore. In some cases, approval will be delayed while the government asks for additional evidence, she added.

Criticism of Obama’s actions by Republican candidates could also deter some people from applying, Simpson said. In her group’s discussions with immigrants, “we make it very clear that this is an executive action that could be changed,” she said.