President Biden on Tuesday will announce sweeping new protections for hundreds of thousands of immigrants who have been living in the United States illegally for years but are married to American citizens, officials familiar with the plan said.

Mr. Biden will detail the policy at the White House on Tuesday while marking the 12-year anniversary of the Deferred Action for Childhood Arrivals, or DACA, which protects people who came to the United States as children from deportation, the officials said. They spoke on the condition of anonymity to discuss a policy that had not been formally announced.

Under the policy, undocumented spouses of U.S. citizens will be shielded from deportation, provided work permits and given a pathway to citizenship. Officials briefed on the conversations said it could affect up to 500,000 undocumented spouses, although the exact scale of the program remained unclear.

The White House did not immediately respond to a request for comment.

Marrying an American citizen generally provides a pathway to U.S. citizenship. But people who crossed the southern border illegally — rather than arriving in the country with a visa — must return to their home countries to complete the process for a green card.

That means long separations from their spouses and families. The new program would allow families to remain in the country while they pursue legal status.

Officials briefed on the discussions said the announcement could amount to the most sweeping unilateral move by a president to provide relief to unauthorized immigrants since President Barack Obama implemented DACA.

In a separate move on Tuesday, Mr. Biden is also expected to announce new ways to help people in DACA, known as Dreamers, gain access to work visas.

The decision comes as Mr. Biden tries to strike a balance on one of the most dominant political issues in 2024. Aware that many Americans want tougher policies on the border, Mr. Biden just two weeks ago announced a crackdown that suspended longtime guarantees that give anyone who steps onto U.S. soil the right to seek asylum here.

Almost immediately after he issued that order, White House officials began privately reassuring progressives that the president would also help undocumented immigrants who had been in the nation for years, according to people familiar with the conversations, who spoke on the condition of anonymity to describe private discussions.

The program Mr. Biden is expected to announce on Tuesday is known as “parole in place,” which has been used in the past for other populations, like families of military members. It gives unauthorized immigrants in the United States protection from deportation for a period of time and access to a work permit.

“What the Biden administration is doing may well turn out to be the biggest news for common-sense immigration policy since the DACA program in 2012 helped childhood arrivals stay,” said Mari Urbina, a former senior aide to Senator Harry M. Reid and managing director of Indivisible, a progressive nonprofit.

Republicans have already assailed the policy.

“This is an attack on Democracy,” Stephen Miller, the architect of former President Donald J. Trump’s anti-immigration policy, said on social media on Monday.

The action could, however, help Mr. Biden in battleground states, like Nevada, Arizona and Georgia, each of which has more than 100,000 voters who live in “mixed status” households, according to the American Business Immigration Coalition, which represents hundreds of companies and supports the proposed policy change.