The statistics say that it should be a rout, that Republicans can't make it a close race for mayor in a city where Democrats outnumber them 4 to 1, where a GOP nominee hasn't won in the last half-century.

But the pundits, and insiders working with Republican Sam Katz, said that 1999 was going to be different, that the well-funded and battle-tested GOP candidate would have an even chance of upsetting Democratic nominee John Street.

With less than four weeks until Election Day, it looks like the pundits were right.

The Daily News/Fox 29 Keystone Poll of likely Philadelphia voters showed the race between Street and Katz is a dead heat, with Katz at 39 percent, Street at 38 percent and a substantial 23 percent undecided. Katz's tiny edge is well within the poll's 4.3 percent margin of error.

The poll was conducted by the Center for Opinion Research at Millersville University, Oct. 1-4, among a random sample of 520 likely voters.

The pollsters used a multi-racial group of interviewers and sampled nearly 50 percent more likely voters than the Keystone poll conducted during the spring primary. The results were nearly identical with internal polls from both campaigns and with independent surveys that officials have been discussing privately.

The poll found that Katz has been able to make a race of it by winning the backing of some 60 percent of Philadelphia's white Democrats.

It suggests that in an election where neither candidate has made even subtle appeals to racial pride or fears, skin color remains the most important factor in determining which candidate Philadelphians support.

Overall, Katz has a sizeable lead among white voters, 67 to 14 percent.

With Street, the numbers are almost a mirror image, as he wins among black voters, 66 to 13 percent.

"This is not a racially divisive campaign, but what's going on here is a familiar pattern of ethnic groups and racial groups supporting people with common characteristics," said Terry Madonna, the poll's director. "It's like ethnic politics, writ large."

That wasn't the only interesting trend in the race.

Katz's recent endorsements by defeated Democratic primary candidates John F. White Jr. and Happy Fernandez seem to be helping the GOP candidate's rise.

The poll found that those who voted for White in the primary are also going for Katz by 37 to 24 percent, with 39 percent undecided. Among Fernandez's small but loyal following, the numbers are even more pronounced, with Katz leading 69 to 15 percent. When all voters were asked, 19 percent said White's endorsement made it more likely they'd vote for Katz, but 4 percent said it made it less likely, and 8 percent said they didn't know.

And although Democratic runner-up Marty Weinberg endorsed Street, his overwhelmingly white, rowhouse voting bloc is even more solidly behind Katz, 83 to 14 percent.

The poll seems to show that support is more solid right now for Street than for Katz, with 80 percent of Street's supporters saying they are certain to vote for him on Nov. 2, while only 72 percent of Katz' backers said the same.

Larry Ceisler, the Democratic political consultant and Fox-TV analyst, said it's not surprising that Street would show some continued weakness after an onslaught of negative ads by Weinberg in the primary, and that the final weeks of the race may now have some potential upward movement for the former City Council president.

"There's not that much bad news left out there on John Street," said Ceisler, referring to the ads that showed a much younger Street shoving a reporter and spoke of his past money problems. "This is about as low as it goes."

The tight race has to be a disappointment to Street and his supporters. The Democratic candidate, endorsed by the popular Mayor Rendell, seemed to be riding a wave of goodwill after besting Weinberg and three others in May, and privately aides spoke of internal polls that showed Street ahead by 30 and then 20 percentage points.

But even then, most experts thought the showdown with Katz, who unsuccessfully ran for mayor in 1991 and for governor in 1994, would tighten, and Street's campaign seemed to suffer from a summer lethargy that peaked when White, once a political ally, crossed party lines to back Katz.

Yesterday, some Street aides were agreeing privately with what some political experts were saying publicly, that poll numbers showing the race a dead heat might serve as a wake-up call to Street's Democratic base.

"I think the Street campaign can look at this as a blessing," said Ceisler, who said too many Democrats may take victory for granted after the party's 12-in-a-row winning streak that started in 1951.

The poll numbers and the closeness of the race highlight the key roles that some swing groups of voters will play over the next four weeks.

Consider the role of Jewish voters, who were given credit for boosting the candidacy of Democratic incumbent W. Wilson Goode over Republican Frank Rizzo in the city's last close general election, in 1987. This year, Jewish voters are heavily behind the GOP's Katz, by 46-14 percent.

While Street enjoyed a 45-27 lead among voters who identified themselves as liberals, 29 percent remain undecided, providing another battleground for the candidates.