DALLAS — Heroin use increased more than 80 percent nationwide from 2007 to 2012, driven by ample supply and a crackdown on prescription narcotics, mayors and policy leaders from across the country were told Sunday.

The leaders attending the U.S. Conference of Mayors in Dallas were also told physicians in the U.S. prescribe enough painkillers to medicate everyone in the country 24 hours a day for a month.

Nationally, the number of heroin users rose from about 373,000 to 669,000 in 2012, according to surveys from the federal Substance Abuse and Mental Health Services Administration.

The increase is “fueled by a growing supply from South America and the crackdown on prescription drug narcotics that has pushed addicts to seek old-fashioned alternatives,” said Mayor Ashley Swearengin of Fresno, Calif., who was chairman of a panel at the conference.

Michael Botticelli, acting director of National Drug Control Policy for the White House, told the mayors that 80 percent of heroin users start with prescription drugs.

He recommended communities and law enforcers work with the public health sector and insurance companies to treat addicts: “We cannot arrest, prosecute or incarcerate addiction out of people.”

Prescription drugs are the most common cause of overdoses in the U.S. — 60 percent of the 38,329 overdose deaths in 2010 were caused by pharmaceuticals, according to the federal Centers for Disease Control and Prevention. In comparison, 3,094 people died of heroin overdoses that year.

Botticelli said the Obama administration’s response to prescription drug use focuses on education, improving prescription drug monitoring, proper medication disposal and enforcement.

He said education includes training physicians.

Education is the solution for law enforcement as well, said Ronald Davis, director of the Office of Community Oriented Policing Services in the Justice Department.

“We can’t arrest our way out of it, but there also has to be an accountability measure. So we can’t avoid that road and we should not,” Davis said. “But it should be fair. It should be balanced.”

Another speaker, a former heroin dealer who started selling when he was 16, said a key way to prevent drug abuse is to give children facts about the dangers of drugs and provide positive mentors.