MAYOR NUTTER was explaining yesterday how he would stuff $13 million in federal money into city potholes at the same time that Joe Biden unveiled phase two of the recovery act.

They talked about the same American Recovery and Reinvestment Act funds. But they were separated by 150 miles and roughly $800 billion.

The mayor, speaking next to a patch of landscape that needed repaving, announced plans to resurface 23 miles of city streets and bring 1,500 curb cuts up to Americans with Disabilities Act standards.

"This project is what the recovery act is all about," the mayor said, "putting people to work and making a real difference.

"With this $13 million, we will repave streets in neighborhoods across Philadelphia, putting 160 people back to work."

On Capitol Hill, Vice President Biden was citing what he called "undisputed" evidence that projects like the one that the mayor announced had already pumped 150,000 new jobs into a struggling U.S. economy.

You can't prove it by this repaving project. The contractor who wins the bid may use 160 workers. But how many of those jobs will be new or permanent?

How many of the 625,000 "new" jobs that the Obama administration expects to create with the second phase of the stimulus package will actually cut into the billowing unemployment rate?

Biden made an admirable attempt to answer those questions in his conference call with reporters yesterday. He said something about multiplier effects and spinoffs. He could almost hear our eyes glaze over.

"I'm a little above my pay grade as I try to explain this," he admitted at one point.

He might want to work on that. It's going to come up a lot. People want to know how or even why you would spend $800 billion for one million jobs.

Biden had just emerged from convening a meeting with the president's Cabinet where each cabinet secretary was asked to identify his top priorities.

He whittled their list down to what he called "the 10 most significant projects" to be funded by the recovery act over the next 100 days.

"We call it the road map to recovery," he said of their plans to fund what he calls "out-the-door, in-place" projects.

But you'd need a GPS to follow this road. The city and federal governments have Web sites meant to help us follow the money as it is being spent.

Whitehouse.gov/recovery and the city's Phila.gov/recovery are set up to track spending by federal and city agencies. But they don't quite.

An even more elaborate attempt to keep us posted will be up and running next month, Biden said.

He promised that it will record "every federal dollar spent in any ZIP code"in America.

"The Council of Economic Advisers pairs projected and actual spending with direct reporting from recipients," Biden said. "They even have a measure built in to account for part-time and seasonal jobs so we don't overcount."

What it shows, Biden said, is "how many jobs would have been in the labor market without the recovery plan. That's fairly simple to track."

It is if you know how to separate out those projects that would have been done even without the stimulus funding. The mayor's repaving project may be a case in point.

It is part of his overall goal to repave 110 miles of bad road in the city. Without a stimulus package, these 23 miles of "federal aid" streets that the mayor identified probably would have been done with federal highway funding.

In effect, stimulus funding allows cities and states to substitute federal dollars for money they would have had to spend anyway.

"There are requirements that prohibit you from using these funds to supplant other funding," said Luke Butler, from the mayor's office of communications.

"This project is within the requirements."

Biden acknowledged that there may be some unanswered questions. But he closed with a flourish.

"Economists on both sides of the aisle point out that without this stimulus package, we'd be a lot worse off," Biden said.

"There's no doubt that the unemployment rate would be considerably higher." *

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