State Treasurer Bob Casey yesterday urged U.S. Sen. Rick Santorum, R-Pa., to disavow an independent group's TV ad that lauds the incumbent's position on Social Security.

Mr. Casey, a Democrat who hopes to unseat Mr. Santorum in next year's election, said that Mr. Santorum should call for the ad to be taken off the air because its sponsor, a group known as Americans for Job Security, declines to identify its donors.

He charged further that the ad distorts Mr. Santorum's position on the controversial issue. And in a news conference Downtown, Mr. Casey raised questions about similarities between the TV commercial and an Internet ad on the Social Security issue, posted on the Santorum campaign's Web site.

"Sen. Santorum and his supporters are not being honest on who paid for these ads and who these people are and he's not being honest about his record on Social Security,'' Mr. Casey said.

He maintained that both the campaign and third-party ads were attempts to obscure Mr. Santorum's position on Social Security. He charged that their focus on a "guarantee'' to seniors was "a smoke screen'' to obscure that Mr. Santorum was a consistent advocate of President Bush's proposals to replace part of traditional Social Security with private or personal accounts for younger workers.

Asked to offer his own prescription for the Social Security system, Mr. Casey declined to offer specifics but said that federal fiscal discipline would allow the country to "grow the economy and reduce the deficit, and when that happens, you can have a bipartisan solution.''

Under federal campaign laws, it would be illegal for a campaign to coordinate advertising or other election activity with a third-party group like Americans for Job Security. Asked if he was charging that the Santorum campaign had violated federal campaign regulations, Mr. Casey said, "I'll leave that to the lawyers.''

Robert Traynham, the Santorum campaign's communications director, dismissed Mr. Casey's complaints, assuring reporters that "in no way, shape or form did we coordinate these ads.''

Mr. Traynham stood on Ross Street outside the Casey press conference offering an instant rebuttal to the Casey complaints along with his own charge that the Democrat was pursuing what he characterized as a negative campaign.

The ads that sparked yesterday's exchange include superficially similar sunlit images of senior citizens that appear while narrators point to a legislative proposal sponsored by Mr. Santorum for Congress to guarantee Social Security benefits for older workers.

Mr. Casey noted that beyond their broad similarity, both ads include shots of what appears to be the same older man and young boy walking hand in hand.

John Brabender, Mr. Santorum's media strategist, said the overlap came from stock footage that his agency purchased from the archives of Getty Images.

Michael Dubke, president of Americans for Job Security, said the group's ad was produced by the Washington media firm The Stevens and Schriefer Group and also included stock footage from Getty Images.

Like Mr. Traynham, Mr. Dubke denied any contacts between his group and the senator's campaign. He said his group decided to air the ad "because ... the politicians and the elites of this country are going to be focused on Pennsylvania'' because of the Santorum-Casey contest.

Americans for Job Security has sponsored an advertising campaign advocating generally conservative positions on fiscal issues, including permanent repeal of estate taxes in states across the country. Mr. Dubke said that his group would consider sponsoring more ads in Pennsylvania during the next year. He said the group declined to identify its donors because "we want our issues to be the point of discussion.''