For example, she proposed to match contributions by small donors with additional taxpayer funds, which would in theory diminish the influence of big donors by enhancing the collective financial clout of small ones. Her campaign did not offer many specifics for such a system, such as the amount of the match or — more crucially for critics — what such a program might cost.

Mrs. Clinton’s announcement was hailed by supporters of tighter financial rules for candidates, who have struggled to make political money a burning campaign issue despite surveys showing widespread disgust with existing rules.

“What she has proposed is both good policy and good politics,” said David Donnelly, the president of Every Voice, a Washington group that supports tougher campaign-finance and influence-peddling restrictions. “That’s why Clinton should actively campaign on this platform and push these solutions to the center of the debate in the days, weeks and months to come.”

Mrs. Clinton’s efforts to address the issue come even as she works to help Priorities USA Action, the main super PAC supporting her candidacy, raise hundreds of millions of dollars to compete with Republican groups that have far outraised their Democratic counterparts. Last month, Priorities said it had secured $20.5 million in commitments since July.

Republican critics were quick to call Mrs. Clinton’s plan hypocritical. “Hillary Clinton stopped making calls to her own super PAC donors long enough to call for an end to super PACs,” said Jeff Bechdel, a spokesman for America Rising, a conservative super PAC.

But Democrats say forgoing super PAC money would be tantamount to handing the election to Republicans, erasing any chance for reform.