Ms. Carroll said on Saturday that she had not been watching the television coverage or the president’s response to her allegations but that friends had informed her about Mr. Trump’s comments.

“This is what happens to women who come forward,” she said.

Ms. Carroll, 76, is the author of “Ask E. Jean” in Elle magazine. Her forthcoming book, “What Do We Need Men For?,” is expected to be published by St. Martin’s Press next month. In it, she describes being harassed and mistreated by a series of men, in addition to the accusation against Mr. Trump.

Ms. Carroll wrote that Mr. Trump asked her to try on lingerie that he was considering buying as a gift.

Once they entered the dressing room, according to Ms. Carroll, Mr. Trump pushed her against the wall, pushed his mouth against her lips, then pulled down her tights, unzipped his pants and forced his “fingers around my private area, thrusts his penis halfway — or completely, I’m not certain — inside me.”

Ms. Carroll said she did not come forward earlier because she feared death threats and “being dragged through the mud, being dismissed.”

Mr. Trump has faced allegations of groping and kissing women without their permission and has previously been accused of sexual misconduct. He was heard boasting of sexual assault in a tape from “Access Hollywood,” and Ms. Carroll’s account will most likely reignite the discussion over those previous allegations and Mr. Trump’s treatment of women.

In an interview with a reporter during a campaign event in South Carolina on Saturday, Mayor Bill de Blasio of New York, who is running for president, said he would investigate Ms. Carroll’s account if she files a formal complaint with the police. But experts say the statute of limitations may prevent a case from going forward.