The process is so cumbersome that a growing number of elected state officials, medical experts and members of Congress have started calling for loosening the restrictions. In June, a letter signed by 30 members of Congress, including four Republicans, called the extra scrutiny of marijuana projects “unnecessary,” saying that research “has often been hampered by federal barriers.”

“It defies logic in this day and age that marijuana is still in Schedule 1 alongside heroin and LSD when there is so much testimony to what relief medical marijuana can bring,” Gov. Lincoln Chafee of Rhode Island said in an interview. In late 2011, he and the governor of Washington at the time, Christine O. Gregoire, filed a petition asking the federal government to place the drug in a lower category. The petition is still pending with the D.E.A.

Despite the mounting push, there is little evidence that either Congress or the Obama administration will change marijuana’s status soon. In public statements, D.E.A. officials have made their displeasure known about states’ legalizing medical and recreational marijuana.

The agency’s position seems at odds with that of President Obama, whose Justice Department has allowed states to legalize either medical or recreational marijuana as long as they follow certain federal priorities, such as not allowing sales to juveniles. Mr. Obama has also said that he believes marijuana is no more dangerous than alcohol and that he is bothered by the disproportionate number of minorities incarcerated for possession of the drug.

Asked if there was an inconsistency between the president’s stance and that of the Drug Enforcement Administration, a White House spokesman, Matt Lehrich, said: “The administration’s policy continues to be that while the prosecution of drug traffickers remains an important priority, targeting individual marijuana users is not the best allocation of federal law enforcement resources. The D.E.A. is carrying out that policy.”

There are signs, though, of a possible shift in attitude within the federal government. In May, the D.E.A. issued new rules to increase the government’s production of marijuana for research this year to 650,000 grams from 21,000 grams.