John Street, who took his first jab at mayoral rival Sam Katz in a TV ad over the weekend, threw a left hook at the GOP candidate yesterday.

The Democratic nominee called Katz's school voucher proposals "a reckless and radical plan" and challenged him to a debate that would focus largely on the concept, in which parents of private and parochial school kids get government grants.

"I know that Sam Katz has never spent one day in public office," Street said in a statement faxed to reporters late yesterday. "But even political candidates ought to be held accountable for their proposals."

The statement came just hours after Street appeared before a group of leading black Baptist ministers and played up Katz's ties to the GOP, saying Katz would "support a Republican philosophy" and raise money for its candidates.

The Katz campaign accused Street of a low blow with the statement. "It may have been easy for John Street to be a demagogue as president of City Council, but as a candidate for mayor it's much harder to fool voters," said Bob Barnett, Katz's campaign manager.

Barnett said Katz wants more money for Philadelphia public schools in addition to trying out a voucher program, and noted that Street - despite calling vouchers "reckless" - said earlier this month he could support them as part of a hypothetical deal with Harrisburg to get more school funds.

The Katz spokesman also suggested that Street and his aide were playing political games by challenging his rival to a debate before the Pennsylvania chapter of the National Coalition 100 Black Women on Oct. 26, more than four weeks from now.

He said Street already knew that Katz had told the group he wants to come on a different night - because that is the night the local Republican Party has its fund-raiser.

The release came just a day after Street debuted a TV ad slamming Katz both for vouchers and for calling for cuts in tax money for schools in 1994.

Street was forceful in linking Katz to the GOP when he appeared in person before the Baptist Ministers Conference at the 2nd Mount Zion Baptist Church in West Philadelphia.

He also told the black ministers they had an obligation to fight apathy and to make sure that members of their congregation vote on Nov. 2.

"Their failure to go to the polls and vote is offensive to their Christian duty and responsibilities," Street said.