In a rare foray into a congressman's ethical conduct, Obama told NBC's "Today" show that Weiner's sexually charged photos and messages online to several women was "highly inappropriate."
"I think he's embarrassed himself. He's acknowledged that. He's embarrassed his wife and his family. Ultimately, there's gonna be a decision for him and is constituents. I can tell you that, if it was me, I would resign," the president said in an interview to air Tuesday morning.
Obama said public service "is exactly that, it's a service to the public. And when you get to the point where, because of various personal distractions, you can't serve as effectively as you need to at the time when people are worrying about jobs, and their mortgages, and paying the bills, then you should probably step back."
House Minority Leader Nancy Pelosi has called for Weiner to quit, as have several other Democrats including party chairwoman Debbie Wasserman Schultz.
The House Ethics Committee on Monday began a preliminary inquiry that could bloom into a full investigation if Weiner, a New York Democrat, ignores calls to resign.
House officials told The Associated Press that the ethics inquiry is not yet extensive, and committee leaders have not indicated whether they will order a more intensive staff investigation. The officials requested anonymity because the committee has not announced the staff inquiry.
If Weiner did resign, the committee would no longer have jurisdiction to investigate him. If he remained in Congress, Ethics Committee Chairman Jo Bonner of Alabama and ranking Democrat Linda Sanchez of California could name a four-member subcommittee to conduct a more thorough investigation. That could lead to an ethics trial.
The Ethics Committee is not designed as a quick-reaction force when a scandal erupts. An investigation could last months, even longer, if the case became legally complicated and Weiner decided to mount a full defense.
If the committee decides that a member violated the rules, its options include issuing a written rebuke, recommending the House vote to censure the lawmaker or recommending expelling the member by a two-thirds majority.
Congress returned to work Monday as Weiner began a leave of absence while seeking treatment for an undisclosed disorder at an undisclosed location. House members can seek leaves of absence, which are routinely granted, and the House approved without objection a two-week leave for Weiner at the close of legislative business Monday night.
The Weiner scandal, heading into its third week, has been a huge embarrassment to Democrats, who are eager to put the controversy behind them.
Weiner is expected to be a dominant topic when House Democrats meet Tuesday morning. They could try to oust Weiner from the caucus or try to strip him of his committee assignment on the Energy and Commerce panels.
Weiner's vow to seek treatment and to work to repair his tattered reputation did little to ease the furor.
Republicans suggested that Pelosi was not tough enough on Weiner. Michael Steel, a press aide to House Speaker John Boehner, said in an email that Weiner's intention to seek a leave of absence "puts the focus" on Pelosi.
House Majority Leader Eric Cantor, R-Va., who has called for Weiner to resign, said if Weiner does not leave, Democrats should consider taking away his committee assignments.