NEW YORK (Reuters) - Lawmakers in U.S. states that have legalized marijuana criticized the Trump administration on Thursday for cancelling a policy that had kept federal prosecutors at bay, saying the move amounted to meddling in states' affairs and ignored more pressing priorities like the opioid crisis.

The move was announced on Thursday by Attorney General Jeff Sessions, rescinding an Obama-era policy that had eased enforcement of federal marijuana laws amid a wave of legalization in states from Pennsylvania to Alaska. The shift took place just three days after California launched the world's largest regulated commercial market for recreational marijuana.

It was not clear how the move might affect a burgeoning marijuana industry in the six states including California and Colorado that have legalized the drug for recreational use, plus dozens of others that permit medicinal use. The industry is forecast to reach nearly $23 billion in sales by 2021.

"Let me give you a list of things more important for federal prosecutors and federal law enforcement to pursue other than marijuana: 1. Basically anything," Democratic U.S. Congressman Ted Lieu of California wrote on Twitter.

Massachusetts Attorney General Maura Healey, a Democrat, said the move "inexplicably" directed federal law enforcement resources away from an opioid epidemic that she said was ravaging communities.

Republican Senator Cory Gardner of Colorado said the decision on marijuana use must be left up to the states and that the Justice Department had trampled on the will of voters in his state and elsewhere.

States that allow the sale of marijuana for recreational use also include Washington, Oregon, Alaska and Nevada. Maine and Massachusetts had looked likely to follow suit this year.

At the center of the dispute is a policy under Democratic former President Barack Obama, known as the Cole Memo, that directed federal prosecutors not to interfere with state legalization efforts.

Oregon's governor, Democrat Kate Brown, said in a statement that more than 19,000 jobs have been created in her state in a legal market that officials had "worked carefully to build in good faith and in accordance with the Cole Memorandum."

Washington Governor Jay Inslee, a Democrat, said his state's pot laws keep criminals out of the market, and stop the drug reaching children or crossing borders to neighboring states.

"We are going to keep doing that and overseeing the well-regulated market that Washington voters approved," he said.

In Nevada, Republican Attorney General Adam Paul Laxalt said his office was reviewing the Justice Department's letter "and evaluating the ramifications for our State." Governor Brian Sandoval, a Republican, said he believed his state's system was a model for others to emulate.

Bob Troyer, U.S. Attorney for the District of Colorado, said in a statement his office would continue to be guided by the same principles that have long governed all their prosecution decisions: "focusing in particular on identifying and prosecuting those who create the greatest safety threats to our communities around the state."

Sessions' move on Thursday also raised questions about whether federal prosecutors could focus on medical marijuana programs run by states such as Pennsylvania.

Pennsylvania's Democratic U.S. Senator, Bob Casey, said many children were among those in the state being prescribed medical marijuana for serious illnesses, adding the Justice Department's announcement caused "serious concerns."

"Bureaucrats in Washington should not interfere with the medical care these patients are receiving," Casey said in a statement.

But the news was welcomed by critics of cannabis who saw it as a chance to push for a crackdown on the substance, the use of which remains prohibited under federal law.

"We are encouraged," said Scott Chipman, the southern California chair of Citizens Against Legalizing Marijuana. "We'll be meeting with U.S. attorneys in California and elsewhere to talk to them about the havoc being wreaked upon our teenagers and young adults."

(Reporting by Chris Prentice; Editing by Daniel Wallis and Frances Kerry)

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