Yahoo is set to unveil a major marketing campaign to reset advertiser and consumer perception of the long-troubled company during Advertising Week in New York, which starts a week from tomorrow.

According to numerous sources BoomTown has spoken to about the campaign, Yahoo (YHOO) is–at least with advertisers–going to focus on stressing the size and scale of the Internet giant.

The details of the plan will be made public Tuesday, Sept. 22, at a press conference.

It will take place immediately after a keynote speech–titled “Yahoo’s Consumer Revolution…Round II”–that the company’s new CMO, Elisa Steele, is set to deliver on the second day of the Interactive Advertising Bureau’s MIXX conference.

MIXX is a two-day event, run by IAB, focused specifically on online advertising.

Yahoo CEO Carol Bartz is also going to be attending Advertising Week–during which all the major players in the advertising business gather in Manhattan for a series of events–for a plethora of meetings with big Yahoo clients.

It is likely she and several other senior Yahoo execs will be at the press conference, sources said.

That press event will also include Penny Baldwin, a well-known industry exec Yahoo hired as its SVP of global integrated marketing and brand management in July.

The main message Bartz is set to deliver is that Yahoo is a powerhouse unlike any others on the Web when it comes to online display advertising.

And, in fact, Yahoo–despite all the internal and external turmoil it has undergone in recent years–remains one of the largest sites on the Internet, and is the top player in what is also called graphical advertising, as well as online media and communications.

“The whole push seems to be to remind people of vibrancy of the brand and exactly how huge its reach is,” said one person who has seen parts of the presentation. “It is less Yahoo is back than Yahoo has never left.”

Sources also noted that Yahoo is likely to stick to its plan to push the idea of “your home on the Web” to consumers, which I had previously posted about earlier this summer.

The idea of the Silicon Valley icon being the key hub destination for Internet users does dovetail with pushing its size to advertisers–major marketing messages that will also likely cost a pretty penny.

They will have to–Microsoft (MSFT) has been in the midst of a $100 million campaign for its new Bing search site and will likely spend more when it unveils updates to the service, dubbed Bing 2.0–within the next few weeks.

The company showed the changes it showed to its own employees last week, which was the subject of much tweeting on Twitter.

Yahoo will apparently give more specifics as to the spend for the marketing push at the press conference.

But, many sources said, the company is already out in the advertising market now, buying tens of millions of dollars in advertising online and offline to hawk Yahoo in print, on television and elsewhere.

(Full disclosure: Sources said that campaign will include The Wall Street Journal network, which includes this site.)

“It’s dramatic,” said one source about the marketing outlay.

Since she got to Yahoo, Bartz has continually stressed the need to promote Yahoo products and services more, including in an interview last week on CNBC (you can see that longish video here).

And, in the July earnings call for Yahoo, Bartz said: “In addition, we’re hard at work on plans to reposition our most valuable asset: Yahoo’s brand. Our Q3 plans include an initial wave of incremental marketing spend which will increase substantially into Q4 and next year.”

Also, in a Q&A in the same call, she added more about the long-term nature of the spending on branding:

“The branding and our whole campaign of advertising is just starting; however you have to understand that this is an ongoing campaign so it’s not transient at least for the next year or so. We’re really going to move to reposition the Yahoo brand and Yahoo Company, so right now, consider that as cost that’s in the system.”

What Bartz and other Yahoo execs will likely stress less is search, due to the search deal Yahoo struck in July with Microsoft in which the software giant will take over the back-end technology and Yahoo will sell search ads for both companies.

The company will compete with both Microsoft and Google (GOOG) in garnering the search market still, once the partnership is approved by regulators, with Yahoo focusing on differentiating itself via innovative user interface, design, features and functionality.

It is not so apt, if you think about it, that Yahoo has finally put up the details of its new system to let customers buy and sell display advertising–now called APT–right smack in the middle of the most serious financial meltdown of the modern era.

That’s because the economic crisis is likely to become a whirlpool that will be hard for any ad business to avoid, even the often recession-proof digital sector.

But it is Advertising Week in New York and, BoomTown supposes, the show must go on (it’s not as if they could suspend it, like a critically important Presidential debate or anything).

Actually, “ironic,” I suppose, is a better word than “apt,” because the existence of such a system–as a kind of Google-like way to deliver graphical advertising–is extremely vital to the next phase of the online ad game.

In Yahoo’s case, APT would service its sites, as well as big sites like eBay (EBAY) and several hundred newspaper sites, in what one can only hope is a cohesive manner rather than the patchwork way it is done now.

In order to reach many places across the country, for example, a national advertiser now has to potentially make hundreds of buys, which can be highly inefficient.

The other option is to use one of the too-many ad networks. But they often don’t let an advertiser know exactly where an ad is being placed, and it can sometimes create something called “channel conflict” between a publisher and an ad network.

This chaos has long been a problem in the online display business, which has been growing, although not with the same force or overall impact as the search ad business dominated by Google (GOOG).

Thus, the situation begs for clarity and for getting scale built into the system, which can only be imposed by big players like Yahoo (YHOO)–or Google or Microsoft (MSFT), both of which are working on their own systems.

Unfortunately, while the search ad market has a better chance to weather the current economic crisis, the online display market is a horse of a different color.

Many speakers at Ad Week underscored the obvious.

Former Yahoo ad head Wenda Millard, now co-CEO of Martha Stewart Living Omnimedia, said in a panel that the Wall Street crisis will have “pretty severe implications for medium-sized and smaller businesses and consumers.”

It was an opinion expressed by many others in the online space who attended the event, most of whom also tried to note in some fashion that the digital sector has a better chance to weather the expected slowdown than other media like magazines.

That might be so. But as one top digital exec correctly noted to me after the events of this week, which have deeply impacted banks and Wall Street firms, it will be hard to escape the suction-like pull of sinking ships:

“Like it or not, we’re all financial stocks now.”