Sestak spokesman Gary Ritterstein said that Specter was spending money at a "dangerous rate" and that Sestak would be competitive.
Said Specter campaign manager Christopher Nicholas: "The senator is well-situated financially to win a contested primary and then beat the GOP nominee in the fall."
That likely Republican nominee, former Rep. Pat Toomey of Allentown, reported raising $1.67 million in the final three months of 2009 - $4.9 million since announcing his campaign in April. He led either Democratic candidate in recent independent polls.
Democrats are nervous after the GOP victory in a Massachusetts Senate special election 12 days ago, as polls indicate voters are anxious about the economy and alarmed by the growth in federal spending.
Specter, who switched from the Republican Party in April, has the support of President Obama and most Democratic leaders. He also has received endorsements from 310 rank-and-file party activists and elected officials across the state.
After a campaign appearance in Northeast Philadelphia on Friday afternoon, Sestak said he was comfortable with where he stood.
"We know we're going to have enough for what we want to do," Sestak said. At the end of October, he reported $4.7 million on hand.
He said he had held campaign events in 25 counties over the last 22 days. "I'm going to keep banging away," Sestak said. He maintained that Specter's switch was cynical and that primary voters resented the party establishment for lining up behind the incumbent.
Democratic state chairman T.J. Rooney last week bluntly said it was time for Sestak to quit and instead run for reelection to his suburban Philadelphia House seat, because he is only weakening the party.
"It would have been unfair six months ago to say this . . . but we are coming up against it," Rooney told the Patriot-News of Harrisburg. "Will he defeat Arlen Specter in a primary? There's no substantial movement in that direction."