People caught for the first time with a small amount of marijuana in Arlington County, Va., no longer must fear the possibility of jail time. But what’s billed as common-sense reform could have dire consequences for immigrants, both legal and undocumented.

The Arlington General District Court this month imposed the new policy for handling many misdemeanor marijuana possession cases, a change the top prosecutor said would make the court process quicker and less stressful for first-time offenders. But the county’s public defender and immigration advocates are objecting because the shift also means that poor defendants in those cases will no longer get a free lawyer to help them understand — and perhaps fight — the charge.

At issue is the growing divide between the way the criminal justice system and the immigration system treat drug possession. Although many jurisdictions have eased restrictions for carrying small amounts of marijuana and have even legalized possession, immigration laws written at the height of the drug war have not changed.

Because marijuana is still classified federally as one of the most dangerous drugs, illegal immigrants risk being deported if they’re convicted of possessing marijuana — even if it’s their first offense and the amount is small. Legal immigrants who leave the country could be blocked from ­returning.

With a White House that has pledged more deportations and taken a harsher line on marijuana use, advocates fear that a move toward leniency by the local court paradoxically will lead to more ­deportations.

“There’s lots of good reasons for this kind of program,” said Rachel Jordan of the Capital Area Immigration Rights Coalition. “The problem is the unintended consequences for noncitizen residents of Virginia are so harsh that it really needs to be looked at again.”

Across the nation, many prosecutors have announced that they will not seek jail time for marijuana possession, although experts know of no other place where the policy has been codified the same way as in Arlington. Only people facing jail time are entitled to a free lawyer, and advocates say waiving incarceration can actually hurt indigent defendants who opt to plead guilty but may have won at trial.

“It’s a problem creeping up around the country as jurisdictions are strapped for assets,” said Barry Pollack, president of the National Association of Criminal Defense Lawyers. “Particularly in an administration that has promised extremely aggressive enforcement of the immigration laws and an emphasis on deporting individuals who have criminal convictions, the consequences of a conviction can be far greater than a couple days in jail would be.”

Arlington Public Defender Matthew J. Foley said the problems extend beyond immigrants. A criminal conviction can endanger a person’s student loans and driver’s license. It can also lead to harsher sentences after any subsequent conviction.

“It makes it easier to grind people through the system, and there’s no reason for it,” he said.

He is pushing for an agreement that public defenders will be appointed for indigent defendants regardless of whether they face jail time.

Arlington Commonwealth’s Attorney Theo Stamos pushed back against the criticism, saying the new policy is a step forward, not back. Just over the border in the District and Maryland, she noted, it is not a crime to have small amounts of marijuana. Although most people accused of carrying pot will plead guilty, in her view it’s helpful to take away the threat of jail time and get them through the system quickly.

“This is a sensible criminal justice reform effort, and I’m really astounded and confused that the public defender’s office is asking us to impose jail time on their clients,” she said. “The suggestion that somehow these individuals are being railroaded is quite offensive.”

It makes no sense, she said, for prosecutors to pretend they will seek jail time when they have no intention of doing so. She said the change was made by the court, which has the power to decide on appointing counsel. Chief District Court Judge R. Frances O’Brien did not respond to a request for ­comment.

Under the policy, all first-time offenders charged with possession of a half-ounce or less of marijuana will be dealt with separately from other defendants.

Some will be eligible for deferred disposition, which means that if the person complies with certain rules, their charges will eventually be dismissed. But in Virginia, those records cannot be expunged; they will remain public. Those who do not qualify for deferred disposition will be told that they are not facing jail time and thus are not entitled to a lawyer.

Both sets of defendants will be told to come back in two weeks and that, for immigration ­conse­quences or otherwise, they might want to consult an attorney. After a years-long battle waged by civil rights lawyer Victor M. Glasberg, all judges in Virginia tell defendants without a lawyer about the potential immigration fallout of a guilty plea.

But few, Jordan argued, will understand that a conviction dismissed in criminal court will still affect immigration status. An illegal immigrant will be glad to avoid going to jail, where in Virginia a sheriff would notify Immigration and Customs Enforcement of their status. But if he or she is arrested later and taken into deportation pleadings, a guilty or no-contest plea will close off opportunities to stay in the country.

Legal permanent residents would not face mandatory deportation, thanks to a U.S. Supreme Court ruling, but Jordan said that if they leave the country they will not be able to get back in.

“It’s going to hit every type of immigrant, in lawful status or unlawful undocumented status,” Jordan said.

J.D. King, a professor at Washington& Lee School of Law who studies the right to counsel, said nonimmigrants likewiseare usually ignorant of the ramifications of a plea.

“Very few criminal defendants are going to say, ‘Well, wait a second, this is terrible news, I’d rather face the jail time but have a lawyer next to me,’ ” King said. “It solves the short-term problem, but there’s all these other long-term consequences that nobody is advising the client about.”

Foley said the warnings are hardly the same as providing a lawyer, because poor defendants still won’t have the means to hire one.

“It will help no more than a doctor advising an uninsured, cash-strapped patient how to remove his tonsils, set a broken leg or cure his cancer,” he wrote in a letter to Arlington community leaders.

He argues that prosecutors are doing defendants no favors by promising to waive jail time, because, in his opinion, no jury in Arlington would impose a jail sentence for marijuana possession in the first place. And he says his office often successfully contests these cases, such as when marijuana is found in a search of a car that has multiple passengers.

If prosecutors don’t think that marijuana possession cases merit a trial, advocates for legalization say, then they should stop charging them altogether.

“We need to move forward with real decriminalization and not court-sentencing decisions, because you run into these issues,” said Kaitlyn Boecker of the pro-legalization Drug Policy Alliance. “We’re extremely excited that they’ve decided to eliminate jail time . . . but we believe that people should still have access to attorneys, especially because folks arrested on marijuana charges tend to be from marginalized communities.”

From 2003 to 2013, her organization found, marijuana arrests in Virginia increased 76 percent; in Arlington they went up 81 percent.

Several localities across the country have decriminalized marijuana. But Virginia state law blocks local officials from doing so.

Some state leaders, however, appear to be warming to the idea. Senate Majority Leader Thomas K. Norment Jr. (R-James City), a longtime foe of legalization, said last fall that “it’s absolutely crazy that we continue to lock people up for possession of a modest amount of marijuana.” The state crime commission, he said, could study the idea.

But his spokesman soon dampened any hopes of immediate change. “Virginia is a loooong way from changing its drug laws,” he said.