Microsoft Corp. led the market in the third quarter for operating systems used in personal digital assistants, surpassing for the first time the Palm OS that dominated the handheld-computer segment for years.

The Redmond, Wash., company shipped 1.38 million units of Windows CE in the quarter ended Sept. 30, accounting for 48.1 percent of the market, researcher Gartner Inc. said Friday. PalmSource trailed far behind with 850,821 units, or 29.8 percent of the market.

During the same period a year ago, PalmSource shipped 1.2 million units, 46.9 percent of the market, compared with Microsoft's 1.04 million units, or 41.2 percent.

The switch was not a surprise, given PalmSource's focus on supplying an OS for advanced cellular phones, called "smartphones," that contain many of the same features as PDAs, such as contact lists, personal calendars and email. PalmSource's Palm OS is used in smartphones from PalmOne Inc. and Kyocera Wireless Corp.

"They've abdicated their leadership in the PDA market in order to become a significant player in the smartphone market," Gartner analyst Todd Kort said of PalmSource.

The market's No. 3 operating system is from Research In Motion Ltd, which supplies the OS for its own BlackBerry PDA, a device that's popular among businesspeople. OS shipments increased more than 350 percent in the quarter to 565,000 units from 123,775 a year ago. RIM's market share rose to 19.8 percent from 4.9 percent.

Linux was the No. 4 operating system, but its market share dropped to 0.9 percent from 1.9 percent a year ago.

Driven by RIM's success with the Blackberry, the overall PDA hardware market increased in the quarter 13.6 percent to 2.86 million units from 2.52 million units a year ago, according to Gartner. The same driver is expected to account for most of a 4 percent increase for the year to about 12 million units.

Given the PDA market trends, it makes sense for PalmSource to switch its marketing and research and development focus to smartphones. Shipments of the advanced cellular phones are increasing rapidly at the expense of the PDA market, which has been slipping steadily, Kort said. In addition, smartphones have higher profit margins.

"(PalmSource) could fight a little harder, but it's probably smarter to let (market share) slip and put more of the resources on smartphones," Kort said.

RIM's Blackberry is expected to keep the PDA market growing through the first half of next year, Gartner said. In the second half, however, sales are expected to slow, and the overall market is forecast to post a decline for all of 2005.

PDA sales, however, are expected to eventually stabilize within a mature market that's becoming increasingly dependent on businesspeople. Companies are expected to account for 40 percent of sales this year, compared with 29 percent in 2003, according to Gartner.

While consumers can get enough of the PDA's capabilities in a cellular phone, business executives and sales people will prefer the PDA's larger screen for calling up business documents and email attachments while on the road, Kort said.

PalmOne, the largest user of the Palm OS, led the PDA hardware market, but continued to lose market share to other vendors as it too shifted focus to smartphones. PalmOne's share slipped to 26.2 percent from 34.3 percent a year ago.

No. 2 Hewlett-Packard Co. increased market share to 24.2 percent from 23 percent, followed by RIM, which posted a huge jump to 19.8 percent from 4.9 percent. Rounding out the top five were Dell Inc., 6.5 percent from 5.4 percent; and Symbol Technologies Inc., 2.2 percent from 2.9 percent.