BERLIN — Over the past 27 years, whenever Microsoft sold a new version of Windows, the world’s dominant computer operating system, the software releases had seismic consequences affecting hundreds of millions of consumers.

But this time, the debut of Windows 8 on Wednesday will cast an even bigger shadow: The success of the software will largely determine the fate of Microsoft’s struggling cellphone partner Nokia, which has bet its survival on the Windows operating system.

Analysts say that if Windows Phone 8, the mobile version of the software, does what Microsoft and Nokia expect, the cellphone maker, which is based in Espoo, Finland, will solidify its turnaround over the next three years and overtake iOS, from Apple, as the No. 2 operating system behind Android, from Google.

If not, Nokia’s future in the cellphone business, and that of its chief executive, the former Microsoft executive Stephen Elop, the architect of the strategy, will come into question, the analysts said. Mr. Elop said in April that Nokia had suspended development of its Symbian and MeeGo smartphone platforms to focus everything on Windows.

“This is a make-or-break moment for Nokia,” said Carolina Milanesi, an analyst at the technology research firm Gartner in San Jose, California. “Everything is resting on Windows Phone 8. If that doesn’t work, it will cause an existential crisis for the company.”

Nokia’s transition to a Microsoft-centric smartphone business has been costly.

The company has lost €3.9 billion, or $4.9 billion, since announcing the switch in February 2011 as sales of its older-generation Symbian devices, which still make up the majority of its telephone business, plummeted.

In June, nine months after Nokia began selling the first of its Lumia line of Windows smartphones, its total sales had fallen by 19 percent from a year earlier. The ratings agencies Moody’s and Fitch reduced Nokia’s debt ratings to junk status this summer. As of Friday, Nokia had lost 70 percent of its market value since Feb. 11, 2011, the day Nokia and Microsoft announced their alliance.

But the company and analysts are upbeat about Nokia’s chances for survival.

On Wednesday, Nokia is expected to announce at least two new Lumia phones, the company’s first to run Windows Phone 8 software, which will complement four Nokia models already on the market — the Lumia 900, 800, 710 and 610. Those older Lumia models run Microsoft’s Windows Phone 7.5 software and cannot be upgraded to Windows Phone 8.

One of the new Lumia devices will be a top-end device similar to the Lumia 900, according to a person with knowledge of the product who was not authorized to speak for Nokia and declined to be identified. Like other Windows 8 phones, it will be the first Lumia to have a multicore processor, which makes the device faster and more agile in Web surfing and able to present crisper graphics. The second new Lumia will have a price closer to that of the Lumia 610, which sells for about €190 in Europe.

Nokia is also expected to signal on Wednesday that it is prepared to reduce prices on some existing Lumia models to sustain sales during the transition to Windows 8. It may also announce enhancements to Lumia’s security and encryption features to lure potential business customers of BlackBerry devices made by Research In Motion, the struggling Canadian company.

Jo Harlow, the Nokia executive vice president in charge of the company’s smartphone business, said the new Microsoft software, the first to be developed with input from Nokia, would increase the desirability and demand for the Lumia smartphones.

“The visibility that is going to be created for the Windows user interface, which is the same as that used for Windows Phone 8, is going to create momentum in the marketplace and generate awareness of the platform, where there had not been much awareness in the past,” Ms. Harlow said Friday.

Ms. Milanesi, the Gartner analyst, said Nokia would be helped by the use of multicore processors, which are already standard in smartphones made by Apple, Samsung and others; by enhancements to the Windows scrolling tile interface; and by changes making it easier for software developers to create applications that connect Windows computers, phones, tablets and other devices.

But a cutting-edge smartphone platform will not be enough, she said.