Ever since a Daily News/Fox 29 Keystone mayoral poll revealed that he and financial whiz Sam Katz are neck and neck, John Street, who ruled City Council with his legendary control of the city budget, seems to have lost the will to do his math homework.

Street's Blair Witch-style TV attack ad claims that Katz's plan to reduce the wage tax to 4 percent by 2004 will cost the city "half a billion dollars" in lost revenue - damaging public safety, senior citizens' tax breaks and the public school system.

Would that be Street-supported Doctor of Cosmetology David Hornbeck's public school system?

Isn't that like worrying about "damaging" warm mayonnaise?

Street's alarmist ad stops just short of predicting that if Katz is elected, a plague of locusts will devour Fairmount Park and the Schuylkill will turn into blood.

Daily News reporter and plague expert Paul Davies went to Street's headquarters and asked him how he came up with "half a billion dollars."

Street replied, "What did you get?"

Davies said, "With all due respect, it doesn't matter what I got. How'd you arrive at half a billion dollars?"

Street said his people had worked on the numbers.

His people later faxed over a spread sheet of unexplained numbers - not one of which was half a billion dollars.

Street's surreal "half a billion" scare tactic reminds me of those artificially-inseminated test scores that Street-supported Doctor of Cosmetology Hornbeck hypes to disguise the fact that students are flatlining on the state's reading and math tests.

"Street was the bully of City Council and could therefore deliver 17 votes," Katz told me, "but his knowledge of the budget and his ability to manage money is dismal. That 'half a billion' number and his scare tactics are intellectually dishonest. And he seems to have no remorse about being intellectually dishonest."

Katz said that by 2004, his tax cut would reduce city revenues by less than half of Street's advertised "half a billion" - a less-than-3 percent drop in an over-$10 billion dollar bucket.

Last night, between campaign stops, Street backed off his "half a billion" and said, "It's hundreds of millions. No one believes you can do that credibly without goring somebody's ox."

How much goring, exactly? "I think every one percent is $267 million," Street said. "I can't remember all this stuff. I've looked at so many numbers. You look at four tenths of one percent, you're not looking at a couple of thousand dollars there. If I were at the office, I could put my hand on it. I just can't remember what it is."

Today, Katz releases his tax cut plan.

Tonight, I'll check Fairmount Park for locusts. Might find a few. But not half a billion.