President Trump intends to again extend the deadline for when TikTok must be separated from its Chinese owner, ByteDance, or face a ban in the United States, its third reprieve this year.

Karoline Leavitt, the White House press secretary, said on Tuesday that Mr. Trump would sign an executive order this week giving TikTok 90 more days — to mid-September — to find a new owner to comply with a federal law that requires the company to change its ownership structure to resolve national security concerns. The previous deadline is set to expire Thursday.

“As he has said many times, President Trump does not want TikTok to go dark,” Ms. Leavitt said in a statement.

Mr. Trump has repeatedly declined to enforce the law, which the Supreme Court upheld in January after Congress passed it with wide bipartisan support last year. The app’s future is part of the discussion in his administration’s ongoing trade talks with China.

Mr. Trump, who issued similar delays in January and in April, has given TikTok an unexpected lifeline after its future in the United States appeared to be doomed. The president tried to ban TikTok in his first term but flipped his stance on the app last year — a shift that is credited in part to one of his donors, who has a sizable stake in ByteDance, as well as his own growing popularity on the app.

The repeated extensions have raised concerns among a handful of lawmakers, who have urged Mr. Trump to clarify his plans for TikTok or force it to stop operating in the United States. They and others in Washington worry that TikTok could hand over sensitive U.S. user data to Beijing, like location information, or that China could use TikTok’s content recommendations to sway opinions and spread misinformation in the United States.