The public financing system for presidential campaigns, a post-Watergate initiative hailed for decades as the best way to rid politics of the corrupting influence of money, may have quietly died over the weekend.

Senator Hillary Rodham Clinton of New York became the first candidate since the program began in 1976 to forgo public financing for both the primary and the general election because of the spending limits that come with the federal money. By declaring her confidence that she could raise far more than the roughly $150 million the system would provide for the 2008 presidential primaries and general election, Mrs. Clinton makes it difficult for other serious candidates to participate in the system without putting themselves at a significant disadvantage.

Officials of the Federal Election Commission and advisers to several campaigns say they expect the two candidates who reach Election Day 2008 will raise more than $500 million apiece. Including money raised by other primary candidates, the total spent on the presidential election could easily exceed $1 billion.