Washington (CNN) -- President Barack Obama said Friday that he would strike down a ban on same-sex marriage if he were on the Supreme Court, and that he believed his administration was obligated to weigh in on a California case before the justices.
Speaking to reporters at the White House, Obama opened up about his rationale for signing off on a government brief that was filed in an appeal of California's 2008 prohibition of same-sex marriage.
The Justice Department brief submitted on Thursday urged the high court to invalidate the ban.
"Let's treat everybody fairly. Let's treat everybody equally," Obama said.
The issue could be a defining moment in Obama's presidency, similar to the political impact last year when the high court upheld the health care reform law that he spearheaded.
It is rare for a president to become personally involved in the legal and political considerations in a Supreme Court appeal, and sources say Obama spent a good deal of time reading up on the issue and articulating his views privately before the brief was filed.
The administration is not a party in the California appeal, one of two same-sex marriage cases before the high court this term, and was not required to offer an opinion although the Justice Department often does so in important constitutional cases.
Sources said Obama made the final decision for the administration to submit a viewpoint and signed off on the wording.
He said Friday that he believed it was "important for us to articulate what I believe and what this administration stands for."
The California law, known as Proposition 8, does not provide any rationale for "discriminating against same-sex couples," Obama said.
When faced with a question of whether that's constitutional, Obama said it was "important for us to answer" honestly.
"And the answer is no," he said.
Obama once supported only civil unions, but he described his position as evolving and declared during last year's election campaign he was personally comforable with letting gays and lesbians marry.
The president further raised expectations of an expanded view in the sweeping rhetoric of his inaugural address in January.
Much of the reasoning in any government brief would, in large part, reflect Obama's personal thinking, gained from his years as a former constitutional law professor.
He offered a studied analysis of the issue.
"What we've said is that same-sex couples are a group, a class that deserves heightened scrutiny. The Supreme Court needs to ask the state why it's doing it, and if the state doesn't have a good reason, it should be struck down. That's the core principle, as applied to this case," Obama said Friday.
"Now, what the court may decide that if it doesn't apply in this case, it probably can't apply in any case," he continued. "There's no good reason for it. If I were on the court, that would probably be the view that I would put forward. But I'm not a judge, I'm the president."
CNN Supreme Court Producer Bill Mears contributed to this report.