More than a year before the first primary ballot will be cast, Sen. Arlen Specter is running television ads depicting a likely Republican opponent, Pat Toomey, as a Wall Street insider bent on consigning Social Security to the whims of the stock market.

Christopher Nicholas, Mr. Specter's campaign manager, said the sharply negative ad is airing on cable television across the state, with a total buy of roughly $100,000.

Mr. Toomey, a former congressman, protested that the ad is factually inaccurate, adding, "This is a desperate and silly attempt by Sen. Specter to change the subject away from his support for Wall Street bailouts and massive new spending and debt in Washington."

Mr. Toomey, president of the conservative Club for Growth, fell just short of wresting the Republican nomination from the incumbent in 2004. After considering a run for governor, he has switched his sights to a 2010 Senate rematch. He has yet to formally announce his candidacy but has said repeatedly in recent weeks that he is likely to enter the race.

Peg Luksik, a conservative activist and former gubernatorial candidate, has declared herself as a candidate along with Larry Murphy, a retired Air Force officer.

The early assault on Mr. Toomey comes after a tumultuous legislative span for the veteran Republican. Mr. Specter stirred long-festering conservative resentment when he was one of only three Republicans who voted for the Obama administration's stimulus package earlier this year. Then, in March, he announced his opposition to a high-profile proposal designed to make it easier for labor unions to organize new workplaces.

Mr. Toomey cited the stimulus vote as the catalyst for his renewed interest in running against Mr. Specter.

The anti-Toomey ad invokes his past career as an investment banker in an attempt to define him in the public eye before he has a chance to do so himself. A recent poll suggests Mr. Toomey's potential vulnerability to such tactics. The Quinnipiac University survey, released last week, found that despite his statewide race five years ago, Mr. Toomey is relatively unknown to the public. When asked whether they viewed the former congressman favorably or unfavorably, roughly three out of four Republican voters said they did not know enough about him to express an opinion.

Mr. Specter's own favorable/unfavorable rating among Republican voters was 29 percent to 49 percent in the Quinnipiac results.

Responding to the ad, Mr. Toomey said that one of its key assertions -- that he had trade in credit default swaps -- was inaccurate.

"I never sold a credit default swap to anyone in my life,'' he said in a statement. "They hadn't even been invented yet [when Mr. Toomey was a trader.]

Mr. Nicholas refused to retreat on the ad's claims.

"Toomey concedes selling derivatives and swaps and these are what has produced the financial mess,'' Mr. Nicholas said.