Sestak, a second-term congressman who spent Saturday stumping for votes in western Pennsylvania, shrugged off Specter's comments and said they show the fifth-term senator is "desperate" in the home stretch of their campaign.
Specter kicked off a day of appearances in and around his home city of Philadelphia at a rally at a sprawling cargo terminal along the Delaware River, which is being deepened to allow the entry of larger ships in a dredging project for which the former Republican has led the fight over much of his 30-year Senate career. It is expected to create an estimated 125,000 jobs.
"The job's not finished, and I need another term in office to bring these 125,000 jobs to this region," he told reporters just before speaking at a windy, riverfront rally that attracted about 100 union members.
Gov. Ed Rendell and U.S. Rep. Bob Brady were among the elected officials and union leaders who spoke at the rally.
Specter, 80, is endorsed by the Pennsylvania AFL-CIO and is counting on organized labor to help get out the vote Tuesday.
He continued to attack as misleading a Sestak ad that says Specter switched parties "to save one job - his - not yours."
"I put my job at risk" by switching parties in an attempt to stay in the Senate and "keep your jobs and add more jobs," he told the crowd. "I wasn't trying to save my job."
Specter reiterated his claim that Sestak has the worst attendance record among Pennsylvania's 19 representatives.
"At least I vote," Specter said. "We're paid to vote, and he's missed 127 in this session of Congress."
Sestak, 58, a retired Navy vice admiral, spoke before about 50 people at a neighborhood park in Pittsburgh.
Calling himself the "underdog" in a tight race, Sestak asked the crowd to vote for him. He said he believes it's time for a new leadership, and believes Specter can't be trusted because of his party switch.
"I respect the man, but it is time. It is time for a different generation," Sestak said.
Before the rally, Sestak stopped two blocks away at "Jim's Sweeper Shop" where he was greeted by 27-year-old employee Phil Verostko, a former Navy seaman, saluting and standing at attention.
Verostko said he plans to support Sestak because of his support of small business and his military experience.
"Arlen Specter only cares about himself," he said. "I can't support somebody who has been a politician for so long they forget what it's like to be human."
At the Specter rally in Philadelphia, one labor leader said he believed rank-and-file union members would reward Specter for his pro-labor votes and his experience.
"I think that (the primary) will be very, very close, but I think the people of Pennsylvania are smart enough to know they've got somebody who has a proven record for labor," said Danny Grace, secretary-treasurer of Teamsters Local 830.
Associated Press writer Jennifer Yates in Pittsburgh contributed to this report.