In Friday's broadcast, Corbett called that statement "inappropriate." He told the host he thought "a much better analogy would have been 'brother and sister,' don't you?"
That comment went viral on Twitter. Gay-marriage advocates and political opponents pounced.
"Gov. Corbett's statements are shocking and hurtful to thousands of gay and lesbian couples who are doing the hard work of building strong families all across the commonwealth," said Ted Martin, executive director for the advocacy group Equality PA.
In a video statement later, Corbett, sounding contrite, said that his remarks were not intended to offend anyone, and that he apologized if they did. He said he was trying to explain Pennsylvania's law and the groups it bars from marrying.
"I've always been a lawyer, and I think with my legal head all the time," the governor said in the 97-second clip. "Being a politician is second nature, not first nature."
He added that the constitutionality of Pennsylvania's Marriage Law, which bars same-sex unions, is now before a federal court.
"Same-sex marriage is an important issue, and the question of its legal status is one that will be heard and decided upon its merits, with respect and compassion shown to all sides," he said.
His apology did little to stem the criticism and derision directed his way all day. His official Facebook page teemed with vitriolic comments. Some noted that the apology stopped short of saying that the analogy was wrong and that he was wrong to make it.
The gaffe was also a reminder that Corbett, not known for his political subtlety, will have to maneuver gingerly to improve his rock-bottom public approval ratings and ward off an ever-expanding field of Democrats when he runs for reelection next year.
"I've known Tom Corbett for 20 years and know him to be a very decent man," said Charles Kopp, a senior Republican and Corbett confidante. "He sometimes says things off the cuff that he regrets saying almost immediately, and this sounds like one of those instances."
Kopp said Corbett deserves reelection despite "occasional gaffes."
State Republican Party officials said they believed that Corbett's statements spoke for themselves. Elsewhere, there was no dearth of opinions.
Martin said he was pleased that the governor apologized, but challenged Corbett to meet with same-sex couples "to talk about why marriage matters to all Pennsylvania families."
Democrats seeking the gubernatorial nomination also lashed out.
"Gov. Corbett's continued hateful rhetoric regarding same-sex marriage is unacceptable and an insult to thousands of gay and lesbian Pennsylvanians who simply want equality," U.S. Rep. Allyson Y. Schwartz said in a statement.
York businessman Tom Wolf called the governor's remarks "hateful and demeaning," while onetime Environmental Protection Secretary Katie McGinty said they were "proof we need a new governor who respects every Pennsylvanian."
John Hanger, also a former environmental protection secretary, took it a step further, asserting that Corbett's comments are "beneath the dignity of the office of governor and, quite frankly, disqualify him from holding that office."
Pennsylvania law defines marriage as a union between a man and a woman. A bill was introduced this week to change that.
A lawsuit in federal court seeks to overturn the state's same-sex marriage ban. And the Corbett administration is in a separate legal fight with Montgomery County to prevent it from issuing additional same-sex marriage licenses.
To watch Gov. Corbett's interview with WHP-TV in Harrisburg, go to www.inquirer.com/corbettvideo
Inquirer staff writer Amy Worden contributed to this article.