The city's 988,000 registered voters now must choose.

Street, 56, the Democrat, grew up poor on a farm in Swedeland, Montgomery County, became a lawyer and eventually rose to the City Council presidency. Katz, 49, the Republican, was raised in the comfortable Wynnefield section of the city and became an entrepreneur, building a government-advisory firm and packaging financial deals for sports stadiums.

U.S. Sen. Arlen Specter, a Philadelphia Republican who lost a mayor's race by just 1.5 percentage points in 1967, knows the anxiety that Street and Katz will go through on Election Day.

"It's very disconcerting to know that, every minute, voting machines are clicking off your fate," Specter said. "The tension and the anticipation are very strong."

For a month, the polls have suggested that Street and Katz are in a dead heat. But pollsters can only guess at voter turnout, and turnout will decide the election.

Will African Americans  vote in equal percentage to whites? If they do, Street will feel very good about his chances.

Will Katz, a former Democrat, inspire a large turnout in GOP strongholds of the Northeast and Roxborough? If he can do that, he will feel quite good about his chances.

Will anyone, anywhere, turn out in large numbers, particularly if it rains as forecast? Though praised for the moderate, intelligent tone of the campaigns, neither candidate has inflamed voter passion.

If the contest is razor-close, the third candidate on the ballot could become an unexpected factor. The polls suggest that John P. McDermott, the Constitutional Party nominee, will be the classic 1-percenter - the tail on the dog.

But the tail could wag the dog if McDermott, an anti-abortion, pro-school voucher conservative from the Northeast, steals many votes from Katz in that area. That could throw a bone to Street.

Registered Democrats outnumber Republicans in Philadelphia by a 4-1 ratio. No Republican has captured City Hall since Barney Samuel in 1947. Specter, who 32 years ago lost by 10,954 votes - "I remember every one" - came closest to breaking the Democratic monopoly.

Democrats have been going all out to prevent what they see as the disastrous consequences of a Republican takeover, including the loss of power and prestige in the city where the GOP will hold its national convention in June.

Malcolm Lazin, who helped organize gays and lesbians for Katz, called it "a David and Goliath battle" in which "the old guard is pulling out every conceivable stop."

One major Democratic figure after another has come to town to stir up Democratic turnout, a parade that culminated Friday with a visit from President Clinton.

"The Republicans are betting on us not showing up on Tuesday," U.S. Rep. Robert A. Brady, the city Democratic Party chairman, told a crowd of 5,000 that gathered to hear Clinton at La Salle University.

Clinton has done all he can for Street, who until this year was not well known to insiders of his own party, even though he had served seven years as Council president.

The President taped a radio ad. He mailed a letter to voters. He and Hillary Rodham Clinton taped telephone messages. When he came to town, he brought a Democratic icon - Sen. Edward M. Kennedy of Massachusetts.

"This is a young, vigorous, brilliant public servant," Clinton - three years younger than Street - said of his fellow Democrat.

Specter recalled that Democrats brought Vice President Hubert H. Humphrey to Philadelphia in 1967 to campaign for the Democratic incumbent, James H.J. Tate.

Clinton's possible impact in a tight race should not be dismissed by Republicans, he said. Nor, Specter said, should the Democratic power structure - its ward leaders, its unions, its elected officials.

"The imponderable," Specter said, "is the strength of the Democratic organization."

Rep. Chaka Fattah, a Democratic congressman from Philadelphia, said: "If there's a home court advantage, Street has it. . . . It doesn't assure victory, but it provides a benefit."

Katz's light schedule Friday included greeting morning commuters at the busy corner of Broad Street and Olney Avenue, a few blocks from La Salle.

With him was former Democratic mayoral candidate John White Jr., who in September crossed lines of party, race and a long friendship with Street to endorse the Republican.

That endorsement gave Katz a spike in the polls. It sent a message to swing voters - liberal Democrats, most of them white - that it was OK for them also to cross party and racial lines.

The White endorsement was one of several factors that have enabled Katz to make a race of it.

Street partisans now concede that their man may have blown a chance to put away Katz over the summer. On primary night, May 18, Street told his supporters and a TV audience:

"You know, Democrats are always willing to have a good party primary fight. But we have always had the capacity at the end of that fight to pull ourselves together and get ready for the general election. And I want the city to know that we are about unifying our party."

His instincts were right. But he didn't follow through. He let White get away, and he let former City Councilwoman Happy Fernandez, another defeated rival in the Democratic primary, get away.

Street bristles at the suggestion he let the summer slip away. "We were in a fight to the death" in the primary, he said, while Katz had no GOP opponent. Over the summer, Street said, he did meet with people and did pound away at fund-raising, taking in $400,000 in June alone.

On Monday night, as Republicans gathered at a rented union hall, party leader Michael Meehan stood at the edge of the stage while Katz addressed 1,000 people. The rapture on Meehan's face said he believed the GOP had found a winner at last.

For a generation, his late father, William A. Meehan, had come up short. He had lost the squeaker with Specter. He had lost a close election with Frank L. Rizzo running against Democratic incumbent W. Wilson Goode in 1987.

Now, Michael Meehan sees a good chance.

"I do," he said. "I do."

La Salle University political scientist Ed Turzanski said: "Shame on the Republicans if they don't get their base out, because this is what would be characterized as a historic opportunity."

Though hardly anyone has wanted to talk about it, a big factor in the race is, well, race. The history of Philadelphia politics suggests that the white candidate will get most of the white votes and the black candidate will get most of the black votes.

Each candidate's Election Day operation is designed on racial voting patterns. Each will be a near-perfect opposite of the other.

In the Northeast, where many whites live, the Democrats do not plan to knock on doors or telephone voters to get them out. But Republicans will have several hundred workers knocking on doors and making calls in that area.

In West and North Philadelphia, where many blacks live, the Street operation will be in full force with sound trucks, door knockers and callers. Katz, in contrast, will have people at some polls only to show a presence in the neighborhoods and to answer voters' questions about the candidate.

Neither candidate directly exploited race during the campaign, and both have built coalitions that cross racial and economic lines.

Street and Katz themselves have stuck to issues - the wage tax, school vouchers - in an unprecedented number of debates on TV and in community forums.

On a more nuanced, personal level, the candidates have made each other an issue.

Street, pointing out that Katz has no experience in government beyond a three-year stint on the Board of Education in the early '80s, has regaled audiences about the difference between an experienced cook making macaroni and an inexperienced cook making the same meal. Guess which tastes better?

Katz has characterized Street as a visionless technocrat - a mechanic. He can fix a car, Katz says, but doesn't know where to drive it.