Keep your ear cocked for a giant sucking sound at the center of the Boston office market.

While much has been written about the growing prospect the Hancock tower will wind up being foreclosed on, the real hammer blow has yet to fall when it comes to the gleaming centerpiece of the Hub’s skyline.

As the vultures circle around the stricken sky-blue icon, whoever winds up with the deed to the 60-story skyscraper is going to be faced with the monumental challenge of having to fill a growing mountain of empty office space.

It’s always possible the new owner will bring along a nice capital cushion and can afford take the high road, holding out for the top market rents befitting the city’s most celebrated monument to commerce and capitalism.

But these are not happy times we live in, and owners with big fat bank accounts are hard to find. My bet is whoever buys it is going to have lease up that space fast, and if that means undercutting competing towers with below market rents, so be it.

If the next owner is a lender, as seems increasingly likely, then you can forget about any hopes of a white-knight rescue. Financial institutions that inherit troubled properties tend to cut their losses, whatever the cost to the neighborhood.

The prospect of a new Hancock tower owner desperate to lease space at any price already has downtown real estate executives bracing for the worst.

Just call it the Hancock effect.

Race To Win A Giant Prize

“It will be interesting to see whether they (the new owners) hold rates or crash,” said veteran Boston tower developer Dean Stratouly. “That will ripple right through.”

Right now, New York-based Broadway Partners is still the owner, ostensibly for the next few weeks anyway, of the city’s top office tower.

Whether Broadway can dodge the foreclosure bullet remains to be seen as it engages in last-ditch negotiations with its lenders.

But it doesn’t look too good right now.

Broadway bet big and bet wrong when it shelled out an estimated $1.3 billion for the Hancock back in 2006 amid what looks increasingly to have been a price bubble in the commercial real estate market.

Today, the skyscraper is likely worth less than $1 billion in a declining office market.

Having defaulted on its loan payments, Broadway now faces losing the tower altogether, with a foreclosure auction slated for the end of March.

That has set off a scramble for control of the tower, a field, that so far, is heavy on lenders, including Normandy Real Estate Partners, Black Rock, Petra Capital and RBS Greenwich capital, to name a few.

Whoever takes the keys to the battered Porsche of the Boston office market will inherit one of the tougher repair jobs of recent years.

Nearly 400,000 square feet of space in the Hancock is empty or soon to be, and we are just getting rolling when it comes to this real estate downturn.

And sadly, the tower has lost many of its big names that once made it the place to be in Boston.

It wasn’t too long ago that city’s most powerful executives, David D’Alessandro and Jack Connors, held court at the Hancock tower. No more. D’Alessandro, the former Hancock insurance chief, is long-gone, having first sold the tower and then later his company. The same is true for Connors, with the departure of his ad powerhouse, Hill, Holliday, leaving another gaping hole in the tower.

As long-time corporate tenants have decamped, there hasn’t exactly been a rush to take their place.

The last six months have brought just one major deal, a lease renewal for roughly 91,000 square feet.

The cloud over the tower’s ownership hasn’t helped leasing efforts, notes John Barry, co-founding partner of Richards Barry Joyce & Partners and a downtown office expert.

“There is a sense there is a transition in ownership,’’ Barry said. “It would add a dimension to a negotiation.”

It’s not clear yet what the tower’s next owners will do to fill all that empty Hancock space.

But even in what are likely the waning days of Broadway’s short-lived tenure, the signs are already pointing to a potential fire sale.

Long-gone are Broadway’s hopes of gold-plated, $100-a-square-foot rents. Also gone are all those fancy plans for remaking the plaza in front of the tower and putting some restaurants in the lobby.

Asking rents in the tower are now in the $60-a-square-foot range.

Among downtown real estate executives, the fear now is that once Broadway is gone, that already reduced rate will become the springboard for an even deeper dive down the rental scale.

And as the Hancock goes, so goes the rest of the Boston office market with it.

One top real estate executive, who preferred not to be quoted by name, summed up those market fears rather bluntly: “Rents in the city are going to dive.”