Nancy Pelosi on Monday endorsed Connie Chan, a San Francisco supervisor, in the race to succeed her as the city’s representative in Congress, calling her the candidate who “stands above the rest”.

Pelosi, the first woman to serve as speaker of the House, will retire at the end of her term and had not yet weighed in on the contested primary for the San Francisco district she has held for nearly 40 years. But as early mail-in ballots trickle in ahead of the 2 June primary, Pelosi declared Chan the “leader best prepared to carry forward the fight for San Francisco in the Congress”.

“At a time when fundamental freedoms and democratic values are under assault, we need a leader in Congress who is prepared to fight – forcefully and effectively,” Pelosi said in a letter to residents.

In a video clip released on Monday, Pelosi is seated next to Chan, a progressive Democrat with ties to local labor unions, against a backdrop with an image of the Golden Gate Bridge.

“I know and love this district,” Pelosi says, patting Chan gently on the back. “I know the Congress, and I know Connie. I’m proud to endorse Democrat Connie Chan and ask you to join me in electing her to Congress.”

Pelosi’s endorsement comes as polling shows Chan in a tight contest to advance to the November general election in a field that includes Scott Wiener, a Democratic state senator known for championing legislation to ramp up housing production and enshrining LGBTQ+ rights, and Saikat Chakrabarti, a former tech executive who served as Congresswoman Alexandria Ocasio-Cortez’s first chief of staff and has been an outspoken critic of Pelosi and the Democratic party leadership. Ocasio-Cortez has declined to endorse anyone in the race.

Several recent surveys show Chan effectively tied with Chakrabarti for second place, behind Wiener. Under California’s primary system, the top two contenders will advance to the November general election, regardless of party.

Pelosi has represented San Francisco in Washington since 1987, and remains one of the progressive city’s most prominent – and popular – elected officials.

In her endorsement, Pelosi said Chan brings “important lived experience” as a woman, a mother and an Asian American immigrant to the US.

“Connie’s story reflects the American dream,” Pelosi wrote, “the hopes and courage of so many families who came to this country believing in opportunity, dignity, and democracy.”

Chan was born in Hong Kong and immigrated at the age of 13 with her mother and younger brother to San Francisco, where her family lived in a one-bedroom apartment in the city’s Chinatown neighborhood. If elected, she would be the first Asian American to represent San Francisco in Congress.