WASHINGTON — Sorry, Mr. President.

After nearly single-handedly pushing gay marriage to the forefront of the presidential campaign and inadvertently pressuring President Barack Obama to declare his support for same-sex unions, there was only one thing left for Vice President Joe Biden to do: apologize.

Biden’s mea culpa came Wednesday in the Oval Office, shortly before the president sat for a hastily arranged interview in which he told the American people that he now supported gay marriage.

The vice president expressed remorse and regret for declaring his support for same-sex unions ahead of Obama, said a person familiar with the exchange, speaking on condition of anonymity to discuss the private conversation. Obama accepted the apology, saying he knew Biden had only been speaking from the heart.

Biden’s apology followed days of frustration in the West Wing after the vice president went off script, something he had done plenty of times. Without White House approval, Biden declared on a Sunday talk show that he was “absolutely comfortable” with same-sex married couples having the same rights as heterosexual married couples.

Usually Obama can swat away Biden’s free-wheeling ways. But not this time.

The vice president had publicly broken rank with the president on a politically sensitive issue. And his remarks focused a fresh spotlight on what Obama had vaguely referred to as “evolving” views on gay marriage.

What few people outside of Obama’s inner circle of six or seven close aides knew at the time was that the president had, in fact, finished that evolution months earlier and was waiting for a suitable opportunity to inform the public of his views.

Biden’s comments accelerated those plans.

And they raised questions about political motives when Obama eventually did embrace gay marriage. If Obama had evolved on gay marriage months ago, why had he waited? And if Biden hadn’t spoken out of turn, would the president have spoken out before the November election?

Obama insisted he always planned to talk about his personal views on gay marriage before his party’s convention in early September. And he said he wasn’t angry when told by aides that the vice president had jumped the gun.

But in an interview with ABC News that aired Thursday, Obama did gently chide the vice president, saying that Biden “got a little bit over his skis” in his remarks on gay marriage but that he believed Biden did so out of a “generosity of spirit.”

“Would I have preferred to have done this in my own way, in my own terms, without I think, there being a lot of notice to everybody? Sure,” Obama said. “But all’s well that ends well.”

People close to Biden insist he was simply speaking of his personal beliefs, not trying to push the president to reveal his.

“Joe was being Joe,” said Ed Rendell, the Democratic former governor of Pennsylvania. “He probably wasn’t thinking about the fact that the president was going to make a statement about it on his own.”

And for some White House aides, that was exactly the problem. There was a plan and Biden hadn’t stuck to it.

Biden’s words set off a scramble in the White House. A transcript of his interview with NBC’s “Meet the Press,” taped on Friday, landed on the desks of some top Obama aides in the West Wing. Highlighted in yellow were his comments on gay marriage.

Suddenly it was Biden being showered with accolades by liberals for his bold stance on gay right issues, not Obama, the president responsible for pushing through the repeal of the military’s ban on openly gay service members and ordering the government to stop enforcing the Defense of Marriage Act.

Cleaning up Biden’s mess wasn’t new to the White House. His penchant for gaffes is legendary in Washington and was cause for some concern during the selection process for Obama’s running mate. But over time, Biden’s slip-ups became more of a running joke than a policy problem.

There was the time he was caught by cameras using an expletive to show his excitement over passage of the president’s health care overhaul. And the time he offered his blessings to the deceased mother of the Irish prime minister, only to quickly remember that she was, in fact, alive.

Getting ahead of the president on a politically sensitive issue like gay marriage is hardly just a gaffe. But aides say Biden won’t be punished for his remarks.

While Obama headed to the West Coast on Thursday, Biden was at the White House headlining an event with student groups and higher education organizations. And he’ll soon be back out on the campaign trail raising money for the Obama-Biden ticket.