WASHINGTON, Dec. 14, 2012 -- President Obama says recreational users of marijuana in states that have legalized the substance should not be a "top priority" of federal law enforcement officials prosecuting the war on drugs.

"We've got bigger fish to fry," Obama said of pot users in Colorado and Washington during an exclusive interview with ABC News' Barbara Walters.

"It would not make sense for us to see a top priority as going after recreational users in states that have determined that it's legal," he said, invoking the same approach taken toward users of medicinal marijuana in 18 states where it's legal.

Obama's comments on marijuana are his first following Colorado and Washington voters' approval of Nov. 7 ballot measures that legalize the recreational use and sale of pot in defiance of federal law.

Marijuana, or cannabis, remains classified under the Controlled Substances Act as a Schedule I narcotic whose cultivation, distribution, possession and use are criminal acts. It's in the same category as heroin, LSD and "Ecstasy," all deemed to have high potential for abuse.

Obama told Walters he does not – "at this point" – support widespread legalization of marijuana. But he cited shifting public opinion and limited government resources as reasons to find a middle ground on punishing use of the drug.

"This is a tough problem, because Congress has not yet changed the law," Obama said. "I head up the executive branch; we're supposed to be carrying out laws. And so what we're going to need to have is a conversation about, How do you reconcile a federal law that still says marijuana is a federal offense and state laws that say that it's legal?"

The president said he has asked Attorney General Eric Holder and the Justice Department to examine the legal questions surrounding conflicting state and federal laws on drugs.

"There are a number of issues that have to be considered, among them the impact that drug usage has on young people, [and] we have treaty obligations with nations outside the United States," Holder said Wednesday of the review underway.

As a politician, Obama has always opposed legalizing marijuana and downplayed his personal history with the substance.

Obama wrote in his 1995 memoir, "Dreams from My Father," that he would smoke pot regularly with his high school buddies who formed a "club of disaffection." The group was known as the "Choom Gang," says Obama biographer David Maraniss.

"There are a bunch of things I did that I regret when I was a kid," Obama told Walters. "My attitude is, substance abuse generally is not good for our kids, not good for our society.

"I want to discourage drug use," he added.

While the administration has not prioritized prosecutions of marijuana users and small-scale distributors in states where it's legal, it has not ceased prosecutions altogether. The Justice Department has continued raids on pot providers – including in states where they are legal – in an approach that experts say is more aggressive than Obama's predecessor, George W. Bush.

"I never made a commitment that somehow we were going to give carte blanche to large-scale producers and operators of marijuana – and the reason is, because it's against federal law," Obama told "Rolling Stone" in an interview earlier this year.

It "is a murky area," Obama told the magazine, "where you have large-scale, commercial operations that may supply medical marijuana users, but in some cases may also be supplying recreational users. In that situation, we put the Justice Department in a very difficult place if we're telling them, 'This is supposed to be against the law, but we want you to turn the other way.' That's not something we're going to do."

Obama and the Office of National Drug Control Policy say the negative impacts of widespread marijuana legalization loom large.

Legalization would lower the price of "weed," thereby fueling its use and triggering more widespread negative health effects and subsequent costs of care, the administration says in its official policy position. Officials also say legalization would do little to curb drug violence or eliminate cartels.

"When you're talking about drug kingpins, folks involved in violence, people who are peddling hard drugs to our kids and our neighborhoods that are devastated, there is no doubt we need to go after those folks hard," said Obama.

"It makes sense for us to look at how we can make sure that our kids are discouraged from using drugs and engaging in substance abuse generally," he said. "There's more work we can do on the public health side and the treatment side."

Colorado and Washington are the first states to legalize recreational use of marijuana, presenting a fresh challenge for the Obama Justice Department to navigate in a second term.

While public opinion has shifted toward legalization over the past few years, Americans remain divided about the personal use of pot.

Fifty percent of American adults oppose legalizing the possession of small amounts of marijuana for personal use, while 48 percent would support such a measure, according to a November ABC News/Washington Post poll. The survey has a margin of error of plus or minus 3.5 points.

Colorado Gov. John Hickenlooper, a Democrat who personally opposed legalization, on Monday formally approved the voter-backed amendment to the state constitution legalizing recreational use of marijuana.

The measure will allow individuals to possess one ounce of pot and up to six marijuana plants and licensed stores to sell marijuana starting next year.

Washington State last week officially became the first to allow recreational use of marijuana when a voter-approved ballot measure took effect.

In both states, pot use remains illegal in public. Eighteen states have approved the use of marijuana for medicinal use with a doctor's order. Federal law still prohibits all use and sale of marijuana.

ABC News' Jason Ryan contributed to this report.