Roseanne Barr was at the center of a social media storm on Tuesday after she sent a racist tweet that referred to “The Planet of the Apes” when mentioning a former top adviser to President Barack Obama who is black.

Early on Tuesday, Ms. Barr posted a comment about Valerie Jarrett, the former adviser to Mr. Obama, that said if “muslim brotherhood & planet of the apes had a baby=vj.”

Ms. Barr, whose ABC sitcom closed out a successful comeback season last week, initially dismissed accusations that the comment was racist, defending it as “a joke.” She also said on Twitter, “ISLAM is not a RACE, lefties. Islam includes EVERY RACE of people.”

Ms. Barr subsequently deleted the post about Ms. Jarrett, and initially said nothing about the reference to “The Planet of the Apes.” About a half-hour later, she offered an apology.

“I apologize to Valerie Jarrett and to all Americans,” she wrote. “I am truly sorry for making a bad joke about her politics and her looks. I should have known better. Forgive me – my joke was in bad taste.”

Ms. Barr also said she was “leaving Twitter.”

Ms. Barr’s often incendiary use of the social media platform has stayed in the background amid the success of the “Roseanne” revival.

Months before the show premiered, Ms. Barr said that her children had taken her social media accounts away from her. It was no small matter: She has used Twitter to promote conspiracy theories, and some ABC executives were worried that she might say something offensive enough to lead viewers or advertisers to revolt.

Ms. Barr has been outspoken in her support for President Trump — he called to congratulate her about the ratings for the show’s premiere episode — and her antipathy toward Hillary Clinton.

[Read an interview with Ms. Barr, in which she touches on her and her character’s support of President Trump.]

But as viewers flocked to “Roseanne,” to the delight of ABC executives, Ms. Barr returned to Twitter. None of her posts threatened the show’s success, although some did attract scrutiny. One of Ms. Barr’s messages accused a survivor of the high school shooting in Parkland, Fla., of giving a Nazi salute; another involved a conspiracy theory about Mr. Trump quietly breaking up a child sex trafficking ring including prominent Democrats. ABC was able to sidestep controversy in both instances.

“You can’t control Roseanne Barr,” Ben Sherwood, the president of Walt Disney Company’s and ABC’s television group, said in an interview with The New York Times in March, when asked about her Twitter account. “Many who have tried have failed. She’s the one and only.”

ABC did not immediately respond to a request for comment on Tuesday.

“Roseanne” will probably finish the 2017-18 television season as the No. 3 rated show, behind two NBC programs: “Sunday Night Football” and “This is Us.” More than 18 million people on average have watched “Roseanne” this season, according to Nielsen’s delayed viewing data.

The show was a boon for ABC, and part of a strategy to appeal to viewers in the American heartland. “Roseanne” had nine episodes this past season, and it is scheduled to return in the fall with another 13. When ABC hosted a showcase for advertisers two weeks ago to preview its fall lineup, “Roseanne” took center stage.

“If anyone came to play a drinking game for the number of times we mention Roseanne,” Mr. Sherwood said from the stage at Lincoln Center’s David Geffen Hall, “you’re welcome.”

[The “Roseanne” revival suggested that “as long as you’re good to your neighbors individually, it doesn’t matter how you treat people in the aggregate,” wrote our critic.]

Whitney Cummings — a showrunner for the revived comedy, and one of its most outspoken liberal supporters — left the series this month. In a statement, Ms. Cummings said, “Due to work commitments and my tour schedule, I’m gonna have to watch the Conners from the sidelines next season. It was an honor to work with such an incredibly talented group of actors, writers and crew.”