SAN DIEGO — The Trump administration told a federal judge Monday that the government will not meet Tuesday’s deadline for reuniting all of the children ages 4 and younger who were separated from their parents at the U.S.-Mexico border as part of a crackdown on illegal immigration in recent weeks.

Justice Department lawyer Sarah Fabian said officials have now identified 102 children in that age group and would return at least 54 of them to their parents by Tuesday.

Depending on background checks, the number of young children reunited with their parents by Tuesday could rise to 59, Fabian told U.S. District Judge Dana Sabraw at a hearing Monday morning.

Federal officials have been unable to provide precise numbers of separated children and parents to Sabraw, who is presiding over a class-action lawsuit filed by the American Civil Liberties Union on behalf of the separated families. Lawyers for the government say federal agencies have been unable to locate some parents who were released or deported after being separated from their children. Some are in criminal custody or have criminal records that make them ineligible to immediately claim their children.

But at the hearing, officials said they were negotiating and working together to find parents. Most will be released in the United States after being reunited with their children, Fabian said.

“I am very encouraged about the progress,” Sabraw said at the hearing. “This is real progress. I’m optimistic that many of these families will be reunited tomorrow.”

Sabraw had ordered the government to provide a list of the separated children’s names to the ACLU over the weekend. He scheduled another hearing for Tuesday morning.

Fabian said the parents and children will be reunited in an undisclosed location administered by U.S. Immigration and Customs Enforcement and then released to await immigration proceedings.

“ICE will take custody and then release the parent and child together,” she said. “They will not remain in ICE custody.”

ACLU attorney Lee Gelernt said in court that the government had taken “significant steps” to reunite families but was still in violation of Sabraw’s court order and should be moving more quickly.

“I believe that they can still reunite some [more] individuals by tomorrow,” Gelernt said during the hearing. “We just don’t know how much effort the government’s made to find” the parents.

Sabraw has also ordered the government to reunite nearly 3,000 children 5 and older with their parents by July 26.