Stefano Tonchi has yet to begin his new gig as editor of W magazine, but already his job forecast is full of storm clouds.

After all, since the heady days of 2007, ad pages for the five main fashion magazines — Vogue, In Style, Elle, Harper’s Bazaar and W — have fallen a staggering 31.9 percent. And none of the five titles is down more than W, which has seen 52.5 percent of its ad pages fly away.

Little wonder that Patrick McCarthy, the man who presided over W since 1985, was bumped aside and replaced by Tonchi, who had been editing T, the New York Times fashion title.

Now the question is can W, and the category as a whole, come back.

“Designers will always love fashion books — the readership and environment is irresistible,” said Steve Farella, the CEO of media ad buying agency, Targetcast. But they are not the only advertisers to worry about. “Other marketers to women now have options that may be more immediate, interactive and accountable,” he said.

Even though by tradition, the editor puts together the news and features and the publisher goes out and sells the ads, most expect Tonchi will have to play a big role in the ad sales department.

“They have no margin for error anymore,” said one fashion industry insider. “Selling ads will be his responsibility, building a bridge to advertisers to get them to support his magazine will be his main job,” said the executive.

At the same time, he will have a delicate balancing act.

“Maybe [Condé Nast boss] Si [Newhouse] will let W stay as it is, the edgier little sister title to Vogue. But will Anna Wintour resent that?” asked one fashion executive, who noted that Anna herself has been pushed to make the Condé Nast flagship more commercial.

And the tolerance for long-term losses at Condé Nast is gone.

“Fashion books will always be part of the media landscape but not as many, not as thick and possibly not as frequent,” said Farella. “Only strong brands will survive.”Keith J. Kelly

Manhattan children’s musician Leon Fallon, aka “Outback Aussie,” recently released his first DVD, and if fans of “The Wiggles” get a sense of deja vu while watching it — it should come as no surprise. John Field, the brother of blue-shirted Wiggle Anthony Field, and the writer of more than 250 Wiggles songs, including “Hot Potato” and “Dorothy the Dinosaur,” is the producer.

The DVD is the follow-up to Fallon’s 2007 CD, which has won raves from Brooke Shields and Christy Turlington, both of whom provided jewel-box quotes.

Fallon, of course, is hoping some of John Field’s magic wears off on him.

After all, The Wiggles, whose concert tickets are as hard to snag as those of Madonna, earned $41 million last year and have sold more than 17 million DVDs and videos and five million CDs and cassettes worldwide since they first hit the Australian children’s entertainment scene in 1991.Julie Earle-Levine

Sometimes the NBA Store on Fifth Avenue must feel more alive, and more crowded, than The Garden during a Knicks game — at least to Tracy McGrady.

The Knicks guard, serving as a “new associate” for the day last Wednesday, was mobbed by customers as he worked the store, helping some make their purchases before having a shooting contest with five lucky fans. The winner of the hoops contest, Carlos Vasquez, 26, not only got to brag about his win but also walked away with one of McGrady’s $100 Adidas TS Supernaturals, autographed, which he had worn during the previous night’s win at hone.

“I have no words to describe it,” Vasquez told The Post in an interview Friday. “He’s my favorite player and once I found out via Facebook that he was going to be there, I took off from work and got to the store at 9:30 in the morning” — 30 minutes before it even opened.

Store employees are getting used to seeing NBA players walking the aisles.

Word is, teammates on the 8-63 Nets, Chris Douglas-Roberts and Yi Jianlian, will stop by this week to host a clinic (write in your own jokes here) and that fan favorite John Starks will teach shooting skills on April 1 — and that’s no joke.Richard Wilner

The euro has lost 11.4 percent of its value in the last four months, falling from $1.51 on Nov. 25 to its close at $1.34 on Friday, which could slow the parade of Europeans that have been among the strongest group of buyers of Manhattan real estate in recent years.

But not everyone thinks the slowdown will come.

“The dollar has strengthened substantially against the euro in the past few months, so it is not as good for a European to buy now as it was,” said Paula Del Nunzio, a top broker at Brown Harris Stevens. “But New York real estate remains cheap in the minds of Europeans compared to their capitals, which means that they will continue to buy in New York when they find an attractive property.”Jennifer Gould Keil

President Obama on Friday unveiled a plan to stem foreclosures by helping out underwater mortgage holders. Just how bad off are those whose homes are worth less than what they owe on their mortgage?

Well, First American CoreLogic reports that the average negative equity for an underwater borrower in the fourth quarter was $70,700. That’s the average price of their parents’ house in 1982, according to the US Census. These folks owe an entire 1982 more than what their house is worth. Post staff

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