Nancy Pelosi has a meaty to-do list in her final months in office: Ensure Democrats take back the House of Representatives. Fend off attempts by the Trump administration to make it harder to vote in the midterms.

And persuade San Franciscans to send a local elected leader little known outside the city to replace her in Washington.

Ms. Pelosi, 86, who is finishing her final term in Congress after representing San Francisco since 1987, has never been one to sit back and watch politics play out. This particular campaign is no exception.

She has engaged in the race to a surprising degree, considering that she did not seem to have longstanding ties with her preferred candidate, Connie Chan, a member of the San Francisco Board of Supervisors. Still, Ms. Pelosi has publicly inserted herself in the race and has worked vigorously behind the scenes to get Ms. Chan elected.

Ms. Chan and her opponent, State Senator Scott Wiener, will square off Nov. 3 in an intraparty battle. Like most San Franciscans, both candidates are liberal Democrats and share a disdain for the Trump administration, as well as a desire to expand rights for immigrants and gay and transgender people.

But they represent different camps in the city’s combative political scene, particularly on housing. Mr. Wiener, 56, has gained national attention as a prolific state legislator focused on getting as much housing as possible built. Ms. Chan, 47, has a reputation in San Francisco for regularly blocking housing proposals, which she sees as lining the pockets of developers to the detriment of low-income tenants who could be displaced.

He calls her an obstructionist best known for voting “no,” saying she is trying to keep San Francisco frozen in amber. She calls him beholden to corporations and billionaires.

Enter Ms. Pelosi.

The first woman to serve as the speaker of the House, she stayed out of the primary campaign until the final two weeks, when she endorsed Ms. Chan. Since then, she has hosted a fund-raiser in the Jackson Square neighborhood for Ms. Chan, lent her communications director to Ms. Chan’s campaign and worked the phones to gather endorsements, including an unsuccessful attempt to convince the labor leader Dolores Huerta to endorse both candidates, not just Mr. Wiener.

Mr. Wiener’s camp believes Ms. Pelosi has been motivated less by wanting to elevate Ms. Chan than by seeking to block him from the seat he has long coveted. It was well known in California political circles that he had been eyeing Ms. Pelosi’s seat for years, and he had once vowed not to run until she announced her retirement.

Last October, however, Mr. Wiener refused to wait any longer and jumped into the race before Ms. Pelosi announced her decision.

Ms. Pelosi has given few interviews about the congressional race. But she said this week that her support for Ms. Chan had nothing to do with her feelings about Mr. Wiener.

“Nobody knows Congress better than I do. Nobody,” Ms. Pelosi said. “And I think she would be the best member of Congress.”

Ms. Pelosi answered questions about the race after an event at San Francisco City Hall to herald the 106th anniversary of the certification of the 19th Amendment, which established the right to vote for women.

There, she listed several reasons for her involvement: Ms. Chan is a woman at a time when women are losing political power. The two have long ties to the city’s powerful labor unions. Ms. Chan performed well as the chairwoman of the board’s budget committee. And Ms. Chan worked hard to help pass Proposition 50, the 2025 ballot measure that gerrymandered California’s congressional map to the benefit of Democrats in response to a similar move in Texas that aided Republicans.

The only negative word Ms. Pelosi would say this week about Mr. Wiener was to reiterate her anger over a satirical chatbot his campaign created that was intended to parrot Ms. Chan and always say “no.”

The stunt backfired when supporters of Ms. Chan, who moved to San Francisco from Hong Kong when she was 13, typed in topics not related to policies, such as the word “accent.” The bot responded with lines that included, “I’m afraid my San Francisco accent is so thick I can barely understand myself.”

Ms. Pelosi released an open letter co-signed by numerous San Francisco female politicians and political groups saying that the chatbot relied on “racist, misogynist tropes for cheap political points.” Mr. Wiener apologized and took the chatbot down.

A group of prominent women who support Mr. Wiener held a rally last weekend in Alamo Square to denounce what they viewed as false outrage over the chatbot and promote his record of legislation important to women, including to expand reproductive freedom and health care access.

Susie Tompkins Buell, founder of the Esprit clothing company and a Democratic power broker in California, spoke at the rally and said in an interview later that she was confused about why Ms. Pelosi was going all-in for a less experienced candidate.

“It’s not about any woman. It’s about the right woman,” she said. “Connie Chan is a place where progress goes to die.”

This week, Ms. Pelosi said she held no ill will against Mr. Wiener for anything other than the chatbot.

“I haven’t said anything about her opponent except when he tried to put words in the mouth of a woman, which is something that I have been fighting to protect my whole career,” Ms. Pelosi said.

Some in San Francisco political circles have speculated that Ms. Pelosi was frustrated with Mr. Wiener because his candidacy might have edged out her own daughter, Christine Pelosi, from running for her seat. But Ms. Pelosi said this week that she and her daughter had never talked about a succession plan; Christine Pelosi is now running to fill Mr. Wiener’s seat in the State Senate.

“She wants to have her own path in California, which I love,” Ms. Pelosi said. “There was never any thought that she would run for my seat, although they like to use that because they don’t know what they’re talking about.”

Christine Pelosi, who was at the City Hall event wearing a tiny pin of a famous image of her mother in a red coat and sunglasses, reiterated that she had never planned to run for Congress and added that she, too, was supporting Ms. Chan. “With respect, some of us do things for positive reasons,” Christine Pelosi said.

In an interview, Ms. Chan said she and Ms. Pelosi have talked often in recent months, and that the congresswoman has been generous with her advice. Ms. Chan described filming the endorsement video together as a pinch-me moment.

“Deep inside me, I was thinking, ‘Oh, I only wish my mother was still alive to see this,’” she said.

Mr. Wiener said in an interview that the chatter about Ms. Pelosi’s involvement was a distraction.

“I’m not running against Nancy Pelosi. I’m running against Connie Chan,” he said. “And I’m going to win.”