Pot advocates say they are leery since previous statements from the administration that it wouldn't go after individual medical marijuana users was followed by crackdowns on dispensaries and others who grew and sold the pot.
"There's some signal of hope," said Alison Holcomb, who led Washington's legalization drive, but added that it will take more than the president to clarify the issues around legal pot. "We ultimately need a legislative resolution."
In an interview with Barbara Walters scheduled to air on ABC on Friday, Obama said that going after "recreational users" would not be a "top priority" in the two states, where voters legalized pot use in November.
In his comments, the president didn't specifically address how the federal government would respond to state officials in Washington and Colorado, who are beginning work on regulations for commercial pot sales.
Under the laws, possession of up to an ounce of pot is legal for adults over 21.
The Justice Department has declined to say whether it would file a lawsuit to block the laws, but has said marijuana is still illegal under federal law.
Tom Angell of the group Marijuana Majority said Obama's comment didn't add anything new. He said the federal government rarely goes after users and the president can do more besides passing the responsibility to Congress.
Angell said Obama can use executive power to reclassify pot as a legal drug.
Federal prosecutors haven't targeted users in the 18 states and Washington, D.C. that allow people to use marijuana for medical reasons. However, federal agents have still cracked down on dozens of dispensaries in some of those states.
U.S. Rep. Suzan DelBene, D-Wash., said Obama's statements weren't definitive but could be a sign that the federal government might be willing to work with the states to develop a new regulatory model for marijuana.
"I think the president's comments are a good sign," she said.
Legalization activists in Colorado were frustrated after they tried and failed to get the president to take a stand on the state's marijuana measure during the presidential campaign in the battleground state.
"Here's the president, an admitted marijuana user in his youth, who's previously shown strong support for this, and then he didn't want to touch it because it was such a close race," said Joe Megyesy, a spokesman for a marijuana legalization group.
Megyesy said Obama's comments were "good news," but left unanswered many questions about how pot regulation will work.
Even if individual users aren't charged with crimes, pot producers and sellers could be subject to prosecution and civil forfeiture and other legal roadblocks, he said.
Marijuana is a crop that can't be insured, and federal drug law prevents banks from knowingly serving the industry, leaving it a cash-only business that's difficult to regulate, Megyesy said.
Colorado's Democratic governor, John Hickenlooper, said Obama's statements didn't settle questions about regulating pot.
"If the Justice Department and the president come together and together release a statement along those lines, it would certainly give us some clarity," he said.
Other states have been closely watching the developments in Colorado and Washington and how the federal government responds.
In Delaware, where a medical marijuana program has been put on hold amid concerns over fear of federal prosecutions of pot growers and distributors, Gov. Jack Markell's spokeswoman said his administration has the same concerns about legalization.
"If the federal government is saying it won't pursue persons with a medical need or recreational users, but it is prosecuting persons who provide that marijuana in a safe manner, then we are forcing people to obtain marijuana from the illegal market," Cathy Rossi said.