For months, Mayor Bill de Blasio has ducked questions about whom he would endorse in the Democratic primary for governor. Would he back Gov. Andrew M. Cuomo, with whom he has carried on a bitter feud — or Cynthia Nixon, the actress who was an early supporter of his mayoral campaign and is a close friend?

On Saturday, he finally gave an answer: neither.

“It will be my job to partner with the next governor and lieutenant governor on behalf of the working people of our city,” Mr. de Blasio said in a statement emailed to reporters just after 6 p.m. “New York City must have a voice in state policy that shapes so much of our lives. I believe endorsing a candidate in these races is at this moment counterproductive to that advocacy. My vote Thursday will be between me and my ballot.”

Translation: Mr. de Blasio chose to play it safe. Had he endorsed his friend, Ms. Nixon, it could have further exacerbated his vitriolic rivalry with Mr. Cuomo. In contrast, if he were to endorse Mr. Cuomo, as he did four years ago, he would expose himself to criticism that he was cravenly currying favor with the man he has called an obstacle to progress on many issues — and it could seem a betrayal of his progressive values.

But his caution in making no endorsement at home belies his ambitious positioning as a national progressive leader; he recently created a political action committee, Fairness PAC, to support his national political activities. The PAC has raised more than $71,000 so far, according to campaign finance reports filed with the New York State Board of Elections.