A decision by White to spurn his longtime friend and former City Council colleague John Street and back the GOP's Katz would be a stunning move that would roil the race to replace Mayor Rendell, boosting the chances of the financial consultant seeking to become Philadelphia's first Republican mayor in a half-century.

That's because while White, the former housing chief, captured just 22 percent of the May primary votes, those ballots were concentrated among white liberals and upscale blacks in neighborhoods like Mount Airy, Chestnut Hill, and Center City -- the voting blocs that experts say are going to be the key battlegound in November.

Pundits say that a Katz endorsement by White and a circle of key political and labor leaders who supported him in the spring could signal liberal Democrats that it would be OK to crossover and vote for a Republican candidate for mayor.

"Katz has worked hard," one key White backer said. "Street has worked not as hard."

White and his core group of supporters who have stuck together since the primary and who recently held separate meetings with Street and with Katz are slated to meet again on Monday at an undisclosed location, and sources have said that most of the White team will be recommending an endorsement of the Republican.

A half-dozen members of the group, all of whom talked to the Daily News on the condition of anonimity, cautioned that a decision by White to bolt the Democratic Party in November -- a major move for a lifelong Democrat and an early leader of the city's black political movement -- is by no means a done deal.

Aides to Street, who said earlier this summer that most of White's primary voters will be backing Street in the fall regardless of whom White actually endorses, seemed to dismiss the latest manueverings.

"I find it interesting that John White is still such a story," said Ray Jones, Street's campaign spokesman. He said that the former City Council president is already gaining votes from White's stronghold in Northwest Philadelphia and getting money from some major donors to White's primary campaign.

One thing that is a little surprising about White's flirtation with Katz is that a couple of weeks before the primary, with White gaining momentum after a string of endorsements from the teachers' and city employees' unions, gay activists and others, Katz ran a series of blistering TV and radio ads bashing White's record. Most experts say the Katz ads, which also attacked Democratic runner-up Marty Weinberg, were a thinly veiled effort to guarantee that Street was his fall opponent.

But all of the White supporters who spoke with the Daily News said that Katz has aggressively wooed the group, even visiting White's home to apologize for the ads and courting White's father, a founder of the Black Political Forum and still a force. They said Katz had assured them that he has backed away from some of his past support for privatization of city services that is of concern to unions.

The White allies said that Street, in sharp contrast, has done little or nothing to court the group, and that his apprearance before them a couple of weeks ago was very unimpressive.