The new version will instead be branded Windows 7, because it is the seventh of a long line of operating systems for PCs developed by the company since the 1980s. Thecompany did not say when it would sell Windows 7 to the public.

The company will also announce that it is planning to introduce a Web-based version of its Office Suite of programs, aiming to head off a new wave of competitors like Google Docs and Zoho, which have deployed word processors, spreadsheets and presentation programs that run on a Web browser. The company was vague, however, about how it would price the programs and acknowledged that it would face skeptical analysts who have said they believe the strategy will cannibalize the company’s profitable Office franchise.

After almost two years, Windows Vista still faces a lackluster reception from consumers and a relentless marketing barrage from Apple.

The problem was highlighted last week when Microsoft reported its financial results for the most recent quarter. Its Windows unit reported just a 2 percent rise in revenue against a 4 percent decline in operating income. The computer industry viewed the setback as a shift of historic proportions. The company acknowledged last week that the mix of Windows sales in both mature and emerging markets had tipped more toward low-cost PCs, which come with lower-margin versions of Windows and often not Vista. Sales of Office software rose 23 percent, bringing in more revenue than the operating system

On Tuesday morning, the company planned an extended demonstration of Windows 7 before a group of more than 6,000 programmers attending the company’s Professional Developers’ Conference being held here through Thursday.

The demonstrations will focus on changes around the user’s ability to personalize the operating system and how the user controls the system

“We’ve done a lot of work around how you manage the windows, how you launch programs and how you manage the windows of the programs that you’ve launched,” said Steven Sinofsky, the Microsoft technologist who has led the development of the new version of Windows. “It’s all about personalization and putting you in control of the PC, and that’s a big initiative that we’ve had.”

The demonstration will also focus on how on-screen notifications are handled, an issue that was an irritant for early Vista users who complained about the nannylike behavior of the software.

Mr. Sinofsky, who previously led the development of the company’s Office application, plans on showing Windows 7 running on a low-priced Lenovo notebook computer equipped with just one gigabyte of memory and an relatively low-power Intel Atom microprocessor.

 This suggests that the new version of the program will require far fewer resources than its predecessor, although Mr. Sinofsky declined to make specific performance promises.