In what is sure to be the most expensive Senate race in Pennsylvania history, Sen. Rick Santorum ended June with a fund-raising record and a nearly two-to-one cash advantage over his challenger, Democratic Treasurer Bob Casey.

Mr. Santorum, an underdog incumbent in his quest for a third term, raised $3.6 million in the second quarter of the year bringing his total receipts for this election cycle to $20.1 million. With four months to go before the election, Mr. Santorum had already topped the $19.8 million raised by his colleague, Sen. Arlen Specter, in the 2004 campaign. The Republican entered July with $9.5 million still in the bank, according to figures supplied by his campaign.

With $2.8 million in receipts, Mr. Casey had the most lucrative quarter of his campaign, but his $5.2 million balance, while robust compared to most senate candidates across the country, was still well behind the incumbent. The Democrat's total fund-raising had reached $10.8 million.

Mr. Casey has maintained a lead in another part of the campaign: polling numbers. He has consistently run ahead of the incumbent in public polls of the race. In an average of published surveys compiled by the Web site, realclearpolitics.com, Mr. Casey's lead was 14 points.

While the Pennsylvania Senate race is on pace to set a record for a federal office in the state, it will not set an overall record either nationally, or for the commonwealth.

The total fund raising for Sen. Hillary Clinton, D-N.Y. is already more than $43 million. And in Pennsylvania, taking advantage of the more liberal rules on fund-raising for state offices, Gov. Ed Rendell raised roughly $40 million in winning a primary and general election in 2002.