U.S. President Donald Trump's administration, bolstering his tough immigration stance in an election year, said on Tuesday it will reject any new applications for the so-called "Dreamer" immigrant program and shorten the deportation protections of those whose eligibility is soon to expire.

A senior administration official said there would be a lengthy review of a Supreme Court ruling last month that found the administration had erred in the way that it had decided to end the Deferred Action for Childhood Arrivals (DACA) program, in which some 644,000 immigrants are enrolled.

The administration said it would still consider ending the program, which shields from deportation hundreds of thousands of immigrants living in the U.S. illegally after entering as children – a group often called "Dreamers."

The review is likely to take at least 100 days, putting off any final decision on the program until after the November 3 election in which Trump is fighting for a second term against Democrat Joe Biden. 

As he attempts to close the gap with Biden in the polls, the timing gives Trump breathing room on a program that is popular among many Americans. At the same time, the steps to limit the deportation protections could help to drive up enthusiasm among his core supporters.

Asked at a news conference on Tuesday whether he was still considering a path to citizenship for DACA recipients, Trump said: "We are going to make... the DACA people and representatives happy, and we're also going to end up with a fantastic merit-based immigration system." He did not elaborate.

The administration plans to continue its existing policy of not accepting new DACA applicants, a policy in place since 2017, the official told Reuters. It will extend the eligibility by a year for those DACA immigrants whose protection from deportation was due to expire, as long as they do not have a criminal record, the official said.

The previous policy had been to extend the eligibility for two years.

In addition, a memorandum issued by the Department of Homeland Security said permits allowing DACA recipients to travel outside the country would only be issued in "exceptional circumstances."

"These actions will limit the scope of the program while DHS and the administration review its legality, justifications for a possible wind-down and other considerations relevant to deciding whether to keep or wind down the DACA policy," the official said.

In justifying his concerns about the policy, acting secretary of Homeland Security Chad Wolf said the program was sending "mixed messages" on immigration enforcement.

"DACA makes clear that, for certain large classes of individuals, DHS will at least tolerate, if not affirmatively sanction, their ongoing violation of the immigration laws," the memo said.

Trump has made his hardline stance on both legal and illegal immigration a central platform of his presidency and his 2020 re-election campaign, but DACA is a complicated issue for him because of increasing public support of the program.

A February Reuters/Ipsos poll found 64 percent of adult respondents supported DACA's core tenets. A similar December 2014 poll found that 47 percent of adults supported DACA.

(With input from Reuters)