Former President Donald J. Trump indicated this week that he was likely to back a 15-week federal ban on abortion, with exceptions for rape, incest and life-threatening emergencies.

The comments, which Mr. Trump made Tuesday on the WABC radio show “Sid & Friends in the Morning,” are in line with previous reporting that he had privately expressed support for a 16-week ban. But saying it publicly ties him concretely to a position that has been toxic for many Republicans.

“The number of weeks, now, people are agreeing on 15, and I’m thinking in terms of that, and it’ll come out to something that’s very reasonable,” he said. “But people are really — even hard-liners are agreeing, seems to be 15 weeks, seems to be a number that people are agreeing at. But I’ll make that announcement at the appropriate time.”

He said at the same time that he thought abortion should be a state issue, and added that anti-abortion activists who wanted a ban earlier in pregnancy should understand that “you have to win elections.”

But while Mr. Trump cast 15 weeks as a compromise, such bans are broadly unpopular, according to both surveys and election results.

A KFF poll released this month found that 58 percent of Americans opposed a 16-week ban. In Virginia last year, Republicans campaigned on the 15-week threshold — describing it, as Mr. Trump is doing, as a reasonable middle ground. They lost control of the state’s House of Delegates.

Voters have also consistently expressed opposition to abortion restrictions in states that have put a referendum or constitutional amendment on the ballot, even when anti-abortion activists sought to center the campaign on abortions later in pregnancy.

A 15-week ban would be less strict than the six-week or total bans that many Republican-led states have passed, but it would be significantly more restrictive than the status quo that held for nearly 50 years before the Supreme Court overturned Roe v. Wade in 2022. Roe protected abortion rights until viability, after it was amended by Planned Parenthood v. Casey in 1992. Viability refers to when a fetus can survive outside the womb — which is generally around 23 weeks, though it varies by pregnancy.

Mr. Trump has boasted about appointing three of the Supreme Court justices who overturned Roe. But until Tuesday, he had tried hard to avoid saying what he would do if re-elected, even as his allies went public with their hope that he would use executive actions to effectively ban abortion without legislation.

President Biden’s campaign quickly responded to Mr. Trump’s interview with a statement from Amanda Zurawski, who was initially denied an abortion in Texas despite life-threatening complications and is one of several women suing over Texas’ abortion ban.

“My family has been forever altered by the nightmare that Donald Trump created by overturning Roe,” Ms. Zurawski said, adding, “Trump isn’t ‘signaling,’ he isn’t ‘suggesting,’ he isn’t ‘leaning toward’ anything — he is actively planning to ban abortion nationwide if he’s elected, inflicting the same cruelty and chaos I’ve experienced on the entire country.”