WASHINGTON — Sen. Chuck Schumer apologized today after word got out that he called a flight attendant a “bitch” for ordering him to follow the rules and turn off his cellphone before takeoff.

And his political protégé, Sen. Kirsten Gillibrand, initially provided him with public cover.

Schumer’s outburst was overheard aboard a US Airways flight from LaGuardia Airport to Washington on Sunday.

Schumer and his seatmate, Gillibrand, were chatting on their cellphones when the plane’s captain told passengers to turn them off.

But the two Democratic senators ignored the order and kept talking — prompting a flight attendant to ask them to follow Federal Aviation Administration rules, according to a House Republican aide who was seated nearby.

Schumer asked if he could finish his call. The attendant said “no” because the plane was waiting for him to finish so it could take off. The state’s senior senator ended his call, but then launched into an argument with her, claiming he was entitled to continue his chat until the cabin door was closed.

“She said she doesn’t make the rules, she just followed them,” the aide said, according to Politco.com.

“Bitch!” Schumer remarked to Gillibrand after the attendant walked away.

Gillibrand’s office initially gave Schumer cover, telling Politico.com that the senior senator was “polite” and that “he turned off his phone when asked to.”

Republicans seized on the slip to slam Schumer, circulating copies of news stories about the “b-word” brouhaha.

Once word spread that Schumer had been less than friendly, Gillibrand’s office offered a second statement.

Her aide, Glen Caplin, said: “Chuck did the right thing by apologizing.”

He criticized Republicans for “trying to score cheap political points” from the incident.

After the flare-up was reported, Schumer said he was sorry.

“The senator made an off-the-cuff comment under his breath after the flight attendant walked away. He shouldn’t have made it, he regrets it and he has apologized for it,” Schumer spokesman Brian Fallon said.

The attendant accepted his apology, Schumer’s office said. Schumer went back to Washington from LaGuardia on US Airways yesterday. A flight attendant said he behaved himself.

“He was quiet. He wasn’t on his cellphone or anything,” she said. But other flight personnel said Schumer has a reputation.

“He’s not nice,” said a flight attendant who has served the senator before.