SAN FRANCISCO — Aiming to capitalize on a sluggish response from his rivals for the Democratic presidential nomination, John Edwards is hammering home his opposition to a proposed $20 billion arms sale to Saudi Arabia.

During a campaign swing through California yesterday, the former senator of North Carolina attacked the Saudi arms deal at the outset of his speech to a $15-a-head lunchtime fundraiser at a San Francisco nightclub. A short time later, Mr. Edwards again skewered the proposed arms sale, though no journalist asked about it.

“This is a bad idea for a lot of reasons, including creating an arms race in one of the most volatile regions in the world, escalating the problems with Iran, and on top of the fact that Saudi Arabia has not done the things that it needs to do in Iraq in controlling terrorism,” Mr. Edwards told about 700 of his supporters.

He called on lawmakers to block the arms sale, which is being advanced by the Bush administration. “I believe that Congress’s responsibility is to stop the deal,” he said. While the former senator denounced the proposal quickly after Secretary of State Rice floated it Monday, the two leading contenders for the Democratic nomination, Senator Clinton and Senator Obama of Illinois, have been more circumspect.

Mrs. Clinton has not taken a public position on the arms sale, her spokesman, Philippe Reines, said yesterday.

In a television interview yesterday, Mr. Obama was noncommittal about the deal. “We should not believe arms sales will be a replacement for the hard diplomatic slog we’ve got to go through in the region in order to not only stabilize Iraq, but to make sure Iran and Syria and other countries that historically have been hostile to us aren’t getting stronger,” he told ABC, according to his campaign. “What I worry about is that the administration thinks the way to deal with Syria and Iran is to arm the Sunni governments of Saudi Arabia or Jordan or Egypt,” he added. Mr. Obama also said the impact of the sale on Israel “has to be one of our paramount considerations.”

The major Republican candidates have been quiet about the deal, though a former Massachusetts governor, Mitt Romney, issued a statement yesterday saying the sale should only proceed if the Saudis agree to conditions, such as ending funding for radical schools and mosques.

By emphasizing his opposition to the Saudi arms deal, Mr. Edwards is seizing on an issue that presents an unusual opportunity to make a simultaneous pitch to peaceniks who might oppose any arms sale and to pro-Israel voters who fear bolstering the military of a large Arab state.

“I think it’s bold because a lot of people are still sitting on their hands and trying to decide what they’re going to say publicly about it, not just candidates but also congressional leaders,” a Democratic strategist, Steven Rabinowitz, said. “It sounds like he’s being bolder on the issue than anyone else in the contest.”

Mr. Rabinowitz, a former White House aide who is supporting Mrs. Clinton but is also friendly with Mr. Edwards, said most Jewish support is going to the former first lady, with a smaller contingent backing Mr. Obama.

Mr. Edwards has lagged a bit among Jews, in part due to his selection of a former House leader, David Bonior of Michigan, as his campaign manager. Mr. Bonior was a vocal critic of Israel during his years in the Congress.

Mr. Rabinowitz said the Saudi arms deal could deliver some support to Mr. Edwards. “Does it help him with Jews? Yes. Is it calculated to do that? I don’t think so,” the strategist said.

The reasons for Mrs. Clinton’s reticence on the issue are unclear. President Clinton has maintained close ties with the Saudi royal family. Since leaving office, Mr. Clinton has traveled to Saudi Arabia at least twice. Wealthy Saudis also made major donations to the Clinton Presidential Library in Arkansas.

A New York-based Democratic consultant, Hank Sheinkopf, said he doubted that the Saudi issue would be enough to give Mr. Edwards much traction among Jewish voters. “Is that enough to get them past Hillary to Edwards? That’s going to be tough,” Mr. Sheinkopf said.