Democrat John F. Street pulled the city's diverse Democratic Party behind him to become the first mayor of the next millennium. He scored lopsided victory margins in African American neighborhoods, did well in working-class white wards, and benefited from less-than-enthusiastic turnout in Republican strongholds in the Northeast.

In the end, his opponent, Republican Sam Katz, could not overcome the big Democratic lever - the tendency of Philadelphia Democrats to vote a straight party line.

The high point of Katz's campaign was Sept. 14, when John White Jr., a black Democrat who lost to Street in the party's May primary, endorsed Katz.

White, a former state legislator and state welfare secretary, is popular with African Americans and white liberals - the swing voters in this race. His endorsement of Katz signaled those voters that it was all right to cross party and racial lines - to vote for a white over a black, a Republican over a Democrat.

White's defection seemed to wake up the Street campaign, which had gone quiet over the summer. Street's advertising became more aggressive.

Katz could not pull another John White out of his hat.

All along, the assumption of political analysts was that voters would cast their ballots strictly on racial lines - whites for Katz, blacks for Street. Under this scenario, Katz would win.

That didn't happen. Enough whites stayed with their party to put Street over the top.

From the start, the campaign was a battle for the hearts of Democratic voters.

Katz, whose party is outnumbered 4-1 by Democrats in Philadelphia's voter-registration rolls, needed lots of Democratic votes to win.

Katz made his Republican affiliation seem nonthreatening, even irrelevant. He rarely used the word Republican, rarely appeared with prominent Republicans, and made the most of an endorsement from a leading black Democrat.

Those things helped make the race close.

But Street managed to fire up his core constituency - African American Democrats - in the waning days of the campaign. He cast the election as matter of partisan loyalty, even survival, and brought President Clinton to town to rouse Democrats for a fight.

And those things helped give Street a narrow victory.

Street got the strong African American support he needed. Turnout in black neighborhoods was higher than even his campaign had estimated. In North Philadelphia's 32d Ward, 22 divisions produced 5,200 votes for Street and 223 for Katz.

Katz did well in the Northeast and in South Philadelphia, but not as well as he needed to. While he won ward after ward in Republican strongholds and white Democratic neighborhoods, the margins of victory weren't as high as he had hoped for.

Katz ran a disciplined campaign that sought to play down that he was a Republican and play up his resume as a businessman and deal-maker.

He called himself the candidate of change, the one most able to lead the city into the next millennium, with the vision and skills to reverse the loss of residents and jobs.

For Street, the strategy was to present himself in a new role - as a leader and unifier of the Democratic Party.

Street, in two decades as an elected official, had never run for office outside his Fifth Council District in North Philadelphia and parts of Center City. His ties to the Democratic organization were weak. He had never been a clubhouse Democrat, a gladhander at party affairs.

When he found himself in a tight race with Katz, he needed the party's help and got it. Rep. Robert A. Brady, the city's Democratic chairman, raised money for him and brought the building trade unions into his campaign. The unions' ranks provided a vital source of street workers to get out the vote yesterday in Street's core areas.

The party also delivered major endorsements that underlined the theme that it was crucial for Democrats to vote with their party - and renounce any flirtation with Katz.

Rendell hammered at this theme. District Attorney Lynne M. Abraham, another prominent Democrat, did the same. Then, last Friday, the most prominent Democrat of all - Clinton - came to town for a spirited pep rally where he said it would be an embarrassment for Philadelphia if Street did not win.

Street entered the fall election tired from a brutal Democratic primary in which he drew on every resource he had to beat Marty Weinberg, who captured most of the white rowhouse Democrats - but, like Katz, not quite enough of them.

By the summer, Street's forces were exhausted. Street spent his time raising money for the general election.

His campaign may have been lulled into a sense of security by encouraging poll numbers produced by Street's pollster, Ron Lester, of Washington. Lester, who had never polled a Philadelphia campaign before, told Street he would win easily in the fall, judging from the numbers.

Lester's figures showed Street 30 percentage points ahead of Katz in the summer. This gave comfort to a shy candidate. It also bolstered Street's supporters and advisers, who believed that Street deserved to win - that with his 19 years on City Council, he was the most qualified candidate.

At the same time, the campaign lost some of its edge when key players lost their access to the candidate.

Lawyer Carl Singley, one of Street's closest friends, and Street's advertising and political consultant David Axelrod of Chicago, seemed to lose their places in the candidate's inner circle.

Axelrod's man in the Street camp, press secretary Ken Snyder, quit after the primary. The campaign lost its mouthpiece and, for a time, its contact with the media and the public. Snyder returned in September, after Mayor Rendell became head of the Democratic National Committee and turned the race into a party mission.

The Katz campaign, meanwhile, was on the offensive early on.

Katz began television advertising 14 weeks before the election. He felt he had no choice. He was the underdog, the long shot.

Street went up on television seven weeks before Election Day.

With the early jump on paid advertising, Katz began rising in the polls. He aggressively sought support from white liberal Democrats, whom he considered likely to cross party lines. He reached out to the gay and lesbian community to demonstrate that he was a non-ideological Republican.

Both sides agree that Katz succeeded in his courtship of the white liberal Democrats. The campaigns' nightly tracking polls told them so.

Street was able to stop Katz's rise in the polls in October with ads criticizing him for being in favor of school vouchers and a promise to cut the wage tax to 4 percent by 2004. For two weeks, Street pounded Katz for not coming up with a specific tax cut plan and said that Katz's cuts would devastate city services. Katz finally came out with a wage tax proposal on Oct. 14 but it was light on details.

Instead of detailed discussions of how he would trim departments, he said he would go into City Hall, look at the situation, and make government run more efficiently.

In the final two weeks, the campaign became a battle for blue-collar whites, the same whites who voted for Weinberg in the primary.

Building trade unions and the Democratic Party joined forces to tell those voters in no uncertain terms that they would be traitors if they handed City Hall over to the Republican Party.

Katz was concerned about the blue-collar whites as well and began pitching his advertising toward them with an ad showing a carpenter endorsing Katz.

Yesterday, the strategy on the street for both sides was to pump up turnout in areas of strength - whites for Katz, blacks for Street. And to hold it down in the enemy's strongholds.

Street won the battle on the streets, and with it the election.