After a fall mayoral campaign that has managed to combine obscene expense, good behavior and rich substance, the choice between John F. Street and Sam Katz remains whisker-close - in the polls and on the merits.

Don't heed the juvenile cynics who dismiss the two as bland say-nothings. The men are close on the issues because they're smart and mature on the issues. But differences in style and strategy promise a clear contrast in office.

These candidates turn the knee-jerk cliche - the lesser of two evils - on its head. The hard but welcome challenge here is to pick the better of two goods.

Sam Katz is that man, based on his vivid sense of his hometown's possibilities, his zest for bold action, his potential to attract good people and weave sturdy coalitions. The Inquirer endorses SAM KATZ for mayor of Philadelphia.

The choice hinges on a calculus of hope and risk. It's easy to imagine either man making a good mayor. It's also possible to imagine either stumbling over the obstacle course that 2000 will present: union contracts to bargain, a schools showdown, the spotlight of the Republican convention.

Risk is a word the Street camp wants to plaster on Sam Katz's forehead. It's true he's never held elective office. He is a Republican in a Democratic town. It's possible his wonkish cascade of neat ideas will slow down when it slams into the stone realities of a tight budget and a set-in-its-ways City Hall.

But don't underestimate this wonk. Beneath the glasses, there is fire, there is steel, there is nimble wit and eloquent love of this city. His oratory retains some flabby jargon, but when Sam Katz cranks up his vision for a Philadelphia where people want to live, want to work, want to visit, there's music to make any true-blue Philly heart skip a beat.

The flip side of risk is reward. In this pairing, only Sam Katz has a chance to surprise and soar, to inspire and innovate in the way a gamble named Ed Rendell once did for a desperate city.

Passing over Mr. Street, our clear choice in the Democratic primary, brings a painful knot to the stomach. When the annals of Philadelphia in this century are written, John Street's name will be underlined as a gutsy servant in the city's time of peril. Ironically, the deeds he did while helping to pull the city back from the brink are what permit Philadelphia now to dream the bolder future that Sam Katz envisions.

Going with the new guy poses a risk, sure. Going with Mr. Street poses a subtler risk: While he steered a prudent fiscal course and tinkered with some rough edges of the status quo, Philadelphia's slow-motion crisis of lost population and jobs could grind on past the point of no recovery.

Battles such as those John Street has had to fight in the last decade leave a mark. A certain "been-there-did-that-didn't-work" skepticism seems to cramp his sense of what can be done to make city government leaner and smarter. Old enmities might hamper his ability to shape and move the public will. At times, he's inclined to fight the last war.

One example is the issue the public cares most about: education. The dialogue has finally moved past the appetizer - how the school board gets appointed - to the meat: money; the teachers' contract; vouchers; the fate of David Hornbeck's reform agenda.

For all their sparring, the two men pretty much agree on the goal: a deal with Harrisburg that gives the city schools the money they deserve to consolidate the best of the Children Achieving reforms. Each suspects the deal may require saying good-bye to the impolitic Mr. Hornbeck and hello to some form of vouchers. The difference is Mr. Katz embraces that bargain, while Mr. Street dreams that he can avoid it.

If the vouchers are ample enough to be of use to poor families, Mr. Katz, a former school board member, is right that they're worth a try in return for a major chunk of money for the public schools.

Mr. Street proposes a reprise of the "force a crisis" gambit that crashed and burned once. He can't really explain why it won't also fail the next time.

The milder risk of Mr. Katz's ready-to-deal attitude is that he'll end up settling for less than the schools need. To stiffen his resolve, he should soak up some of his opponent's admirable passion to do right by low-income students.

On education, as elsewhere, the differences between the two boil down to this: Mr. Street's first concern is to meet the needs of people with little choice but to live in Philadelphia, while Mr. Katz looks to meet the desires of those who have the means to leave.

Justice demands that any mayor honor Mr. Street's wish to lift up the ill-served. But Philadelphia cannot thrive, cannot find the resources to help its poor, unless it stops bleeding middle-class families and jobs. Mr. Katz's vision for a city where people with options will choose to live - evident in his stands on vouchers and taxes - is the better path for this moment.

There's risk in the Republican's vow to cut the wage tax more aggressively, but in a city leaking population at an alarming rate, there's risk also in the Democrat's settling for lesser cuts. Mr. Katz's hyped wage-tax "plan" was no such thing, specifying none of the hard trade-offs. But for all its vagueness, his best-practices approach to managing smarter and leaner seems the right direction.

The Katz jobs plan's stress on improving the fundamentals of business climate - taxes, regulations, workforce training and services - is a wise step beyond ad-hoc deal making. On public safety, each candidate passes the basic intelligence test: Keep John F. Timoney, the charismatic and effective police chief.

Mr. Katz promises neighborhoods something that many in The Inquirer's Citizen Voices program ached for: a grassroots process to develop a services plan for each neighborhood, backed up by a contract with City Hall.

In a chief executive's job, good ideas mean little if not linked to the leadership savvy to put them into action. On this score, Sam Katz rises above.

Ready or not, whoever succeeds Ed Rendell will inherit the job of civic cheerleader he turned into an art form. Neither candidate matches Mr. Rendell's earthy charm. But Mr. Katz has a sly wit and a sense of fun. What's more, he grasps the serious purpose behind all that schmoozing, noshing and cannonballing into pools. It builds up good will for when the tough decisions come.

Mr. Street is a cerebral, complex man who can be charming one on one. But pressing the flesh doesn't come naturally to him, nor would the role of national salesman for the city. Sam Katz's dogged salesmanship helped build a company - and has lifted his long-shot mayoral bid to a dead heat in the polls.

That crisp campaign also softens the natural worry about Mr. Katz's political savvy. He's shown deftness in building a multiracial, bipartisan coalition. If he can climb this electoral mountain, he can manage often enough to get the needed nine votes on City Council.

For Mr. Katz to win, many Democrats will have to believe his vow that the "R" next to his name on the ballot is less important than the "Philadelphia" written on his heart. Believe it.

Don't doubt, either, that having a GOP mayor can help unstick the stalemates Philadelphia has endured with the Republican rest of the state over school funding and other unmet needs.

John Street promises a steady hand on the rudder. But Sam Katz offers something beyond that, a fresh wind in the city's sails - ideas and can-do energy that could propel Philadelphia forward.