WASHINGTON -- U.S. Sen. Arlen Specter yesterday joined a top Senate Democrat to call for the creation of a multibillion-dollar public financing program for congressional races.

Mr. Specter, R-Pa., made the announcement one day after confirming that he already has started preparing to run for a sixth term in 2010, citing the exploding costs of modern campaigns and the need to raise tens of millions of dollars to be competitive.

"That time ought to be spent on our official duties," he said yesterday, standing alongside Sen. Dick Durbin, D-Ill.

Mr. Durbin's office estimates that the average cost for the most competitive Senate races in 2006 was $34 million per campaign, double what it was four years before. To keep up, candidates often turn to interest groups for money.

Former Sen. Rick Santorum, R-Pa., spent $28.4 million on his unsuccessful bid for re-election last year, according to opensecrets.org . About 17 percent of his funds came from political action committees. Mr. Specter spent just under $22 million in his 2004 race.

"People who say the public shouldn't pay for elections are missing the point. We already pay for elections," Mr. Durbin said. "We pay when special interests are literally allowed to write their own bills."

The public financing system would provide about $2.8 billion nationwide for each two-year congressional cycle. It would be voluntary.

To qualify as participants, Senate candidates would have to raise $5 contributions from a specific number of supporters, depending on state population.

Pennsylvania's qualification number is 11,000 donors. The state would receive $7.9 million in public funds for the primary election and $19.4 million for the general election.

Some of that money would go to vouchers for television air time, the largest cost for most campaigns.

Mr. Durbin said he expected resistance from both the television industry and many colleagues, who may be reluctant to give up their fund-raising advantages as incumbents. He said he would try to address their concerns.

"This really allows a senator to be a senator and spend less time on the road raising money," he said of his bill.

Rep. John Tierney , D-Mass., is introducing a similar measure in the House.

Nick Nyhart , president of the nonpartisan group Public Campaign, praised the proposed legislation, calling it a "historic opportunity for every elected official in Congress to say 'no' to the politics of big checks and the endless money chase and 'yes' to putting voters first."