State Treasurer Bob Casey won cheers from labor leaders yesterday as he aimed withering criticism at Sen. Rick Santorum; on the state's airwaves, however, the Democratic challenger was the target of a renewed commercial barrage from a conservative group that declines to identify its donors.

Speaking at the state convention of the AFL-CIO in Downtown Pittsburgh, Mr. Casey denounced the Republican incumbent for Bush administration policies ranging from tax cuts to trade agreements.

The Democrat claimed that Mr. Santorum was responsible for the export of American jobs through his support for trade accords, including the North American Free Trade Agreement (NAFTA) and the Central American Free Trade Agreements. Santorum voted against NAFTA and while they have been supported by presidents of both parties, such trade agreements have been consistently opposed by organized labor.

"This state has hemorrhaged jobs heading overseas and this U.S. senator has voted for policies that helped make that happen," Mr. Casey said.

He also said that he would work for better terms in future trade accords that would do more to protect worker rights and safeguard the environment.

The treasurer offered a tacit rebuttal to critics who have contended that his criticisms of the incumbent are seldom accompanied by policy proposals of his own. Mr. Casey noted that he had advocated universal access to early education and called for the repeal of the administration's tax cuts for more affluent Americans.

"Rick Santorum voted for a tax cut for multimillionaires even at a time of war," Mr. Casey added, faulting the Bush administration for the increased federal deficit.

The Democrat made light of the fact that President Bush had visited the region to raise money for the senator at a private event and suggested that his rival was reluctant to be seen with Mr. Bush in view of his lagging poll numbers.

"I thought that was disrespectful to the president," Mr. Casey joked. "They must be worried about something."

Virginia Davis, Mr. Santorum's campaign press secretary, dismissed the Democrat's attacks.

"Once again Bobby Casey is putting politics before service and skipping work to attack Rick Santorum," Ms. Davis said. "Actions speak louder than words, and Sen. Santorum has a long history of supporting policies that strengthen our economy, protect the home land, and improve access to quality health care for all Americans."

While he was being applauded by the union delegates at the Pittsburgh Hilton and Towers, Mr. Casey was being targeted in new television commercials that fault him for being out of the treasurer's office in Harrisburg for nearly half of the time during his initial months as state treasurer.

The ads are sponsored by a group known as Americans for Job Security. The conservative, pro-business group does not disclose its donors, a policy that is legal under the tax code but has been an object of criticism from the Casey campaign.

The ad cites a Philadelphia Inquirer report that Mr. Casey, embarked on his Senate campaign, had been away from his Harrisburg office more than 100 days last year. The Casey campaign has defended his attendance, pointing out that the treasurer has other offices in Pittsburgh and Philadelphia, and that he can be in touch with his office electronically wherever he goes.

"Sen. Santorum's special interest friends are slinging mud in Pennsylvania to cover up for his failed leadership for Pennsylvania and his rubber-stamping of Bush administration policy," said Larry Smar, Mr. Casey's press secretary.

Michael Dubke, president of the Virginia-based group, said it was spending nearly $500,000 on the latest sequence of ads, divided between broadcast stations in Philadelphia and Harrisburg and cable systems throughout the state. This is the third sequence of ads the group has sponsored in Pennsylvania in this election cycle. Previous ads lauded Mr. Santorum's positions on Social Security and taxes. Altogether, the group's spending in the state is approaching $1 million, and Mr. Dubke said that they hoped to spend more as the closely watched race goes on.

The Casey campaign has raised questions on whether the ads had been coordinated with the Santorum campaign, which would be illegal, and has filed a complaint against the private group with the Federal Election Commission. So far there has been no public response to the complaint.

Both Mr. Dubke and Ms. Davis reiterated previous denials of any communication between the campaign and the third party group.

Mr. Casey is considered the prohibitive front-runner for the Democratic nomination to challenge Mr. Santorum, but he faces two opponents in the May 16 primary -- lawyer Alan Sandals and history professor Chuck Pennacchio. The three Democrats will debate for the first time this weekend in Slippery Rock.