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One of the nation's leading experts in Jewish demography recently completed a new study of national Jewish population trends.

It's a bombshell.

Once you've seen it, you can't look at the Jewish future the same way. Simply put, this University of Miami study shows that intermarriage isn't the problem everybody thinks it is.

First, Jews aren't marrying non-Jews at a annual rate of 52 percent. That was a statistical error in the 1990 national Jewish population survey.

The true figure is lower, perhaps much lower. Moreover, surprising numbers of intermarried couples are raising their children as Jews.

The 1990 survey said only 28 percent do so. The new study shows it's as high as two-thirds in some major communities.

The study doesn't draw big conclusions, but they're obvious if you do the math.

America's Jewish community is growing, not dying. Don't pop those corks yet, though. The Miami study's sponsor, the newly formed United Jewish Communities of North America, is sitting on the document.

UJC officials are "reviewing" it and won't predict the publication date.

Only a handful of copies have leaked — "illegally," gripe UJC officials. They won't discuss the contents. For good reason. These are the folks who, in their previous incarnation as the Council of Jewish Federations, brought you that 1990 survey. They've touted it ever since as the biggest and best Jewish demographic study ever done.

The 1990 survey's 52 percent intermarriage figure sparked a nationwide panic over impending Jewish disappearance that continues unabated. They're planning a year 2000 update at 10 times the expense, using the same methods. Now they're sweating bullets because the Miami study raises big questions about their methods.

Partly as a result, UJC decided last month to put the 2000 survey on an indefinite hold — weeks before polling was to begin — over the research department's bitter objections.

Officially, the delay is meant to let the UJC's new committees study the questionnaire. In fact, it reflects new doubts about the 1990 survey. This is serious stuff.

The 1990 intermarriage figure utterly transformed American Judaism. It moved Jewish spiritual survival to the very top of the Jewish community agenda. It put liberals on the defensive. It inflamed communal tensions, as Jewish movements blamed each other for the looming disaster.

Now it appears there's no disaster. Whoops.

The news puts the UJC and its researchers on the spot. And they weren't just wrong. They have fought bitterly to defend their blunder. A few respected Jewish population specialists have challenged the data for years. The CJF-UJC researchers responded by vilifying the critics.

Everyone else kept quiet, convinced it was too complicated to follow, yet ready to believe the worst. The Miami study is different. It merely summarizes local Jewish population surveys conducted in various cities in recent decades.

Its tables compare individual findings from 40 cities, with the 1990 national findings alongside for comparison. Only in passing, in a footnote, is the intermarriage error noted.

"The much cited 52 percent figure for intermarriages would be 43 percent if calculated only for Core Jewish households," writes Ira Sheskin, the Miami study's author.

"Core Jewish households" is survey-speak for homes that contain an actual Jew. Besides Jews, the 1990 survey interviewed hundreds of others who had some Jewish ancestry but never considered themselves Jewish. Inexplicably, the survey included their marriages in the intermarriage rate.

Of course, 43 percent is still high. But that's only the tip of the iceberg.

Critics have found other flaws that exaggerate intermarriage in the survey. Sheskin's comparative charts seem to strengthen some of those claims. In fact, Sheskin's charts make it clear how assimilated American Jews were made to look in the 1990 national survey.

Nearly every one of Sheskin's tables, from intermarriage to Sabbath candlelighting, shows a broad range of religiosity among Jewish communities, from old-fashioned, deep-rooted communities like Cleveland's to newer, more transient ones like Orlando's.

Somehow, the 1990 survey's results always land near Orlando.

That can't be right. Older Jewish communities in the Northeast still outnumber Sunbelt transplants by two to one. The national averages shouldn't resemble Orlando.

Critics also argue that the 1990 survey used mistaken methods that exaggerated signs of assimilation.

The most important of these was data "weighting." All surveys "weight" or overcount responses from blacks, Southerners and rural folks, to compensate for their tendency not to cooperate with pollsters.

But Jews who are black, Southern and rural are more educated and probably more likely to cooperate, not less. At the same time, these three groups are less likely than average Jews to eat kosher food or marry Jews.

According to Hebrew University sociologist Steven M. Cohen, one of the 1990 survey's critics, removing those weights puts intermarriage at 38 percent — a figure now gaining acceptance.

But even that ignores a critical question. What kinds of Jews avoid pollsters? Nobody has ever checked.

Still, certain groups come to mind: the Orthodox, immigrants and Holocaust survivors. Weight those groups more heavily, and intermarriage might be as low as one-third.

The difference is critical.

If half of all Jews marry non-Jews and less than one-third of them raise Jewish children, the prognosis is demographic disaster. That's what the 1990 survey reported, and what most Jews now believe.

But if intermarriage is one-third — and if half the interfaith couples are raising Jewish children — then the community is growing. That's what the Miami study seems to show.

The issue isn't intermarriage alone.

The 1990 survey initially called 125,000 households and asked their religion. About 5,000 said "Jewish." After eliminating false positives — pranksters, schizophrenics, Bible-thumpers calling themselves the children of Israel — they were left with 2,441 inteviewees.

That's how they calculated 5.5 million Jews in America, another sign of stagnation. But they never called back the other 120,000 to weed out the false negatives. How many Jews heard the religion question and simply hung up?

A hint came in 1991, when New York's Jewish federation ran a local population survey. After the polling began, the federation started receiving calls from area police.

The cops were hearing from frantic Jews who thought the PLO was out to get the Jews by pretending to be the UJA. They were wrong. It was the demographers.