SEATTLE — It has not escaped Microsoft's attention that some of the coolest sites on the Web — YouTube and MySpace included — get much of their flash from Flash and other design programs sold by Adobe Systems Inc.

But as Microsoft Corp. gets ready to ship its own line of tools for designers and Web developers, the world's largest software maker finds it must also defend against Adobe on its home turf, the desktop. At the same time, the line between Internet and desktop programs is blurring — and both companies see an opportunity to capture new business.

Microsoft Corp. is preparing to launch Expression Studio, a suite of design software that will go head-to-head with Adobe's flagship tools, Photoshop and Illustrator. It also will include a tool for building multimedia programs to bring it in line with Adobe's Flash. At $599 for the suite, Expression is a steal compared with the $1,000 or more Adobe charges for its Web developer suites.

Expression Web, a Web authoring tool to compete with Adobe's Dreamweaver, is already on the market. Yesterday, the company said its Flash-like browser plug-in, Silverlight, will be released in beta at the end of the month. Both programs enable multimedia presentations that work regardless of the viewer's Web browser or operating system.

Adobe, meanwhile, yesterday started shipping its Creative Suite 3, an upgrade to Photoshop and other core programs. Adobe touted smoother integration with Flash and Dreamweaver, which the company acquired when it bought Macromedia Inc. nearly two years ago.

This is just the latest clash between the two as Microsoft, dominant in operating system and desktop software, sizes up the smaller, Web-savvy Adobe. The software companies also are battling over standards for the paperless office and tools for displaying content on and building applications for mobile phones and hand-held computers.

Microsoft, whose core loyalists are the millions of developers who build desktop programs, has little history with professional designers. While its amateur Web authoring tool, FrontPage, racked up more sales at retail than competing products in 2006, Web professionals have been complaining since the mid-1990s that it doesn't work well with non-Microsoft Web browsers.

This time around, Microsoft said Expression Web will generate HTML and other code that complies with industry standards. It's also discontinued FrontPage.

Forest Key, the creative-sector veteran Microsoft hired to lead the Expression charge, acknowledged that the company is reaching well beyond its traditional base, but said the company needs designers in order to stay competitive as software evolves.

"The state of user experience is just dramatically shifting," said Key.

Expression's tools will also let graphic designers try to create desktop software. In the past, designers worked in Photoshop, then handed a static picture off to programmers, who often had a hard time translating it into a working Web site or application. Expression's programs let designers draw and manipulate images using a familiar interface, but behind the scenes the tools also generate code programmers can work with.