As the mayoral race enters its final laps, Democrat John Street's campaign is hoping that Sam Katz's private lobbying for state tax dollars for a motor track near Reading will throw a monkey wrench into his GOP rival's stretch drive.

Katz's little-publicized push last summer to get $20 million from Harrisburg for the proposed motor-sports park is slammed by Street in his newest TV spot, which began airing yesterday.

"Whose side is Sam Katz on?" the 30-second commercial asks, and it shows Formula One racecars whipping across the screen. "As a businessman, Katz lobbies on behalf of wealthy investors for millions of our tax dollars to fund an auto race track."

"At the same time, candidate Katz is pushing a tax scheme that threatens city services, a voucher plan that would drain money from public schools, even selling PGW, which the Daily News reported would raise rates on senior citizens and the poor," the ad continues.

"Republican Sam Katz," it concludes, as a race car careens into a retaining wall, "The wrong track for working families."

The new commercial puts a new spin on the message that Street has been trying to promote all fall: That Katz's plans for cutting the Philadelphia wage tax below 4 percent would harm city services. The new aspect is to raise doubts about Katz's dealings as a private businessman, a subject most voters know very little about.

Katz and his aides had not seen the new ad, but when topic was described to him Katz said that "it doesn't make sense."

"My job was to provide capital for the project," said Katz, saying there was nothing improper in his lobbying efforts and that he was merely employing the same type of skills he'd likely use as mayor in trying to get private firms and the state to invest in the city.

The area of controversy involves a plan to build the Formula Motorsports Park, a first-of-its-kind type of country club for motor-sports enthusiasts, in a hillside some 40 miles northwest of Philadelphia. The plan featured a 3.1-mile road course for club members.

Last summer, when state lawmakers were studying capital projects that included new stadiums in Philadelphia and Pittsburgh, Katz, listed as chief financial officer, called House Majority Leader John Perzel, a Philadelphia Republican, and asked if the Legislature could include the project. The final bill authorized $20 million for the track - half of its cost, in the form of either a loan or grant - but the money has not been spent, and apparently never will be.

"The raceway project is dead," said Katz, saying that even with the state authorization he wasn't able to get private funding.

Staff writer Joseph R. Daughen also contributed to this report.