As the most expensive mayor's race in Philadelphia history enters its final week, Democrat John Street has hit a theme he likes and Republican Sam Katz hopes to build on the momentum of a powerful endorsement.

Over the next five days, the campaign will see four more face-to-face confrontations between the two men, a presidential visit to boost Democratic fortunes, and a blitz of radio and TV ads to move undecideds and energize each candidates' base.

"Our plan this last week is to just win," Katz said yesterday. "We're going out and getting our voters excited. People are pumped about a real change."

"We're going flat out," Street campaign spokesman Ken Snyder said, "blowing straight through to the finish line."

The Street campaign has settled into a message as the campaign enters its decisive phase: Their man, the Democrat, believes in government that helps poor and working people, in contrast to cold-hearted Republican tax-cutters.

A Democratic mailing to union households in recent days bears the headline "Beware of Republican union-buster Sam Katz." It's one of three that have attacked Katz as one who's reckless plans will destroy the city.

Indeed, Street and his backers have lately begun using the term "rowhouse" as an adjective. Spokesman Snyder referred to Street Saturday as "a rowhouse guy," and Street yesterday spoke of "rowhouse people" who are worried about their future.

It's a term traditionally used as political code for white ethnic working-class folk, a constituency the Democrat needs a piece of to bring home a victory Nov. 2.

Yesterday, Street took his demonstration of blight-removal to Juniata, a largely white working class area, and he will return there again tomorrow.

Katz said yesterday Street's harsh mailings won't work.

"In all these mailings, there are two words you never see - 'John Street,' " Katz said yesterday, "and I think the positive mailings that we're sending out behind his negative mailings are having a tremendous impact."

Katz's ads have been attacking Street's campaign as negative, while responding with counter-arguments to some of Street's charges. Katz will likely keep that up this week, and he will no doubt make heavy use of his endorsement by the Inquirer, published yesterday. The Daily News will endorse a candidate later this week.

Katz plans to stick to his basic message of lower taxes, better schools and safer streets, while trying to fend off Street's continuing attacks.

Street's TV spots, meanwhile, have veered back toward the positive in part, serving up endorsements by prominent local Democrats, emphasizing Democratic themes. And this week, Street will showcase his best endorsement.

"We're unleashing Ed Rendell for the last week," campaign spokesman Snyder said. So look for Rendell on TV and in your mailbox, urging support for Street.

The two campaigns have booked about $1 million in TV commercial time, leaving both camps with the flexibility to run their endorsement pieces and respond quickly to any campaign developments.

And while the two candidates have faced off so often that Katz joked that they suffer from "joint appearance fatigue," there will be four more opportunities to try and score a hard punch or hope your opponent screws up.

Two of the forums, at 9 p.m. tomorrow night on WHYY-TV Channel 12, and 7 p.m. Thursday night on WPVI-TV, Channel 6, will be televised live.

By the time the polls open Nov. 2, it's estimated that all candidates in the primaries and the general will have spent a staggering $25 million on this election.

Street's spending should reach to between $8 and $9 million, with Katz shelling out more than $6 million.