SAN DIEGO — In a sharp rebuke of Sen. Dianne Feinstein, the California Democratic Party has declined to endorse the state’s own senior senator in her bid for reelection.

Riven by conflict between progressive and more moderate forces at the state party’s annual convention here, delegates favored Feinstein’s progressive rival, state Senate leader Kevin de León, over Feinstein by a 54 percent to 37 percent margin, according to results announced Sunday.

Neither candidate reached the 60 percent threshold required to receive the party endorsement for 2018. But the snubbing of Feinstein led de León to claim a victory for his struggling campaign.

“The outcome of today’s endorsement vote is an astounding rejection of politics as usual, and it boosts our campaign’s momentum as we all stand shoulder-to-shoulder against a complacent status quo,” de León said in a prepared statement. “California Democrats are hungry for new leadership that will fight for California values from the front lines, not equivocate on the sidelines.”

A centrist Democrat, Feinstein has long maintained an uneasy relationship with activists who dominate state party conventions, and the vote this weekend — while embarrassing — was not unexpected. The result followed two days of lobbying by the candidates in convention speeches and throughout the convention halls.

In an appeal to thousands of delegates Saturday, de León portrayed himself as an agent of change. He cast Feinstein, without mentioning her name, as a Washington power broker out of touch with progressive activists at home.

“I’m running for the U.S. Senate because the days of Democrats biding our time, biting our tongue, and trying to let it work the margins are over,” he said to cheers. “I’m running because California’s greatness comes from paths of human audacity, not congressional seniority.”

The non-endorsement appears unlikely to immediately alter the trajectory of a contest Feinstein is leading by a wide margin.

First elected in a 1992 special Senate election, Feinstein is out-polling de León 46 percent to 17 percent among likely California voters, according to the most recent poll by the Public Policy Institute of California. Her financial advantage is even more overwhelming: Feinstein held close to $10 million in cash on hand at the end of last year, while de León reported raising just $500,000.

Addressing the convention Saturday, Feinstein reminded delegates of her experience and what she portrayed as a lifetime of service in the cause of Democratic values. She focused heavily on her advocacy of gun control measures, and she urged Democrats to resist splintering in the face of a Republican-controlled Washington.

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California Democrats, she said, have “the largest delegation in the House. You’ve got Kamala Harris and me in the Senate.” She said Democrats can more effectively advance their principles “if we have unified support.”

Feinstein lost the state party endorsement to a rival Democrat, John Van de Kamp, when she ran for California governor in 1990. And though supporters this year waved signs and stopped Feinstein to pose for photographs, she at times appeared out of step working the convention halls.

Interrupted in her convention speech Saturday by music signaling her time to speak had run out, Feinstein said, “I guess my time is up.”

As she left the stage, de León supporters in the crowd yelled back at the 84-year-old, “Time’s up! Time’s up!”

The state party returned a non-endorsement in California’s other major statewide contest, as well.

In the race for governor, Lt. Gov. Gavin Newsom led all candidates with 39 percent support, followed by state Treasurer John Chiang and former state schools chief Delaine Eastin with 30 percent and 20 percent, respectively. Former Los Angeles Mayor Antonio Villaraigosa, who has drawn close to Newsom at the top of statewide public opinion polls, finished a distant fourth, at 9 percent.