SAN DIEGO — U.S. border authorities, in a significant escalation of the Trump administration’s “zero tolerance” immigration policy, are planning to introduce a fast-track prosecution program to criminally charge more people who cross the border into California illegally, according to attorneys in San Diego.

Under the program, called Operation Streamline, migrants will be moved through the criminal justice system in group hearings, with cases handled in a matter of hours, from arraignment to sentencing.

Mass prosecutions of up to 100 migrants per day occur in federal districts in Arizona and Texas but would mark a major shift for California’s southern district, based in San Diego, which hasn’t seen expedited judicial proceedings since the border was overrun with illegal immigration decades ago.

Most people who cross illegally into California are not criminally prosecuted, but the numbers would increase substantially under Streamline.

The plans were recently announced to members of the Criminal Case Management Committee, a group of attorneys, judges and law enforcement officials convened by the district’s chief judge, Barry Moskowitz, to address surging caseloads in the district.

The plans have yet to be finalized, but prosecutors told the committee that they want to charge anywhere from 35 to 100 people per day, including first-time crossers, according to Jeremy Warren, a longtime criminal defense attorney who attended a meeting of the committee Wednesday.

“They want anybody arrested crossing the border to be prosecuted with illegal entry,” Warren said, adding that discussions are still underway on how the court will accommodate the additional cases. Prosecutors want the program to start in one month, he said.

Federal and court officials, including from the departments of Homeland Security and Justice, declined interview requests.

Kelly Thornton, a spokesperson for the U.S. attorney’s office in San Diego, said prosecutors are working with the courts to manage increasing immigration caseloads “in a manner that respects the constitutional rights of defendants.”

The U.S. Border Patrol in San Diego arrests, on average, about 120 migrants per day along the 60-mile stretch it patrols. Cases are rising sharply after the announcement of a zero tolerance policy in April by Atty. Gen. Jeff Sessions.

U.S. authorities say border prosecutions are an effective deterrent, and have made it a cornerstone of President Trump’s efforts to crack down on illegal immigration. Streamline is a U.S. Border Patrol program that requires coordination with U.S. attorneys and federal court judges to set prosecution goals.

It has long generated controversy and protests, with critics calling it “assembly-line justice” that undermines basic rights of criminal defendants.

To deal with rising caseloads, judges in the district at times keep courtrooms open late, immigration agents assist with security, and defendants are shuttled into court from detention centers as far as Arizona.

In a rare step, Moskowitz formed the criminal case management committee last month, including prosecutors, judges, and criminal defense attorneys.

“The increase has and will cause strains, issues and problems for the court and its personnel,” Moskowitz said in his order creating the committee.

The Border Patrol introduced Streamline in Texas in 2005 as a way of penalizing migrants who would otherwise be deported without being charged.

Implementation of the program varies by district, depending on resources and enforcement priorities. Generally, the program aims to increase prosecutions by expediting the judicial process. Within a day of their arrest, migrants appear in courtrooms, where prosecutors offer them misdemeanor plea agreement deals.

The maximum sentence for the crime of “improper” entry into the country is six months, but most defendants plead guilty and are deported after a few days or weeks in jail.

The southern district of California is one of the nation’s busiest, handling significant numbers of healthcare and white-collar fraud cases as well as major gang and drug cartel cases.

The district, unlike those with Streamline programs, has had relatively low illegal border crossing activity for years. Immigration prosecutions were focused on more-serious offenders, including human smugglers and repeat crossers with criminal records.

Defense attorneys have long criticized Streamline, saying it sacrifices constitutional due-process protections for speed.

With several court appearances combined in one, attorneys have limited time to confer with clients that can be complex, they say.

“We’ll defend the cases that are brought, but we don’t want to be in position where we’re processing people like parts in a factory.… People who have been separated from their children are not in a position to make a decision in half an hour,” Warren said.

Charles LaBella, a former senior federal prosecutor in the district, called Streamline “turnstile justice” that is not what the federal courts were meant to do.

“It takes the emphasis off serious criminal aliens and eyes off white-collar criminals, Medicare fraud, bank fraud … to use resources to prosecute misdemeanors against people who are coming to pick fruit or find menial work to send money back home,” he said.

But supporters say the program provides a strong message that the law will now be strictly enforced along the border — a scenario that will deter many people from trying to cross again.

“Most of these folks are not people who want to spend time in jail with a rapist or a drug dealer,” said Mark Krikorian, the executive director of the Center for Immigration Studies, which supports tighter controls on immigration. “They are regular folks, dishwashers, landscapers … for the most part they are not involved in that kind of criminality. But the crime they are committing is sneaking across the border, and the message needs to be sent that this is not something you will be able to get away with.”

Border districts are already showing signs of strain as the zero tolerance policy takes hold. In south Texas, up to 40 shackled defendants at a time appear in courtrooms to plead guilty. In southern Arizona, Chief Judge Raner Collins said the district can’t raise the current limit of 75 defendants per day without getting more resources.

Activists in the past have picketed courthouses and attempted to stop migrant-filled buses from reaching the federal building in Tucson.

Judge Robert Brack, who is believed to have handled more Streamline cases than any judge in the country, recently told The Times that he has decided to step down as a full-time justice in his New Mexico district.

“I have presided over a process that destroys families for a long time, and I am weary of it,” Brack said. “And I think we as a country are better than this.”

richard.marosi@latimes.com

Twitter: @richmarosi