Apple on Thursday pushed back the release of Leopard, the next major upgrade of its Macintosh operating system, until October, saying it had to divert too much of its resources to getting the iPhone out on time.

Because of the delay, consumers ready to buy a Mac, particularly during the important back-to-school season, are expected to delay purchases until the OS's release. Leopard had originally been scheduled to debut in June at Apple's Worldwide Developers Conference.

In a brief statement, the company said the iPhone, introduced at Macworld in January, contained "the most sophisticated software ever shipped on a mobile device, and finishing it on time has not come without a price."

"We had to borrow some key software engineering and QA [quality assurance] resources from our Mac OS X team, and as a result we will not be able to release Leopard at our Worldwide Developers Conference in early June as planned," the statement said.

Instead of the final product, Apple planned to hand developers at the June conference a beta copy of Leopard, with the final release four months later. "Life often presents tradeoffs, and in this case, we're sure we've made the right ones," Apple said.

Nevertheless, the delays are uncommon with Apple, which seldom stumbles in getting out OS upgrades. "It's an unusual turn of events for Apple, which is really good at hitting deadlines with upgrades to its OS, compared with Microsoft," Toni Duboise, analyst for Current Analysis, said.

The biggest impact on Apple will be from missing the back-to-school season that runs from mid-July to mid-September. In terms of computer sales, only the holiday season, which starts the Friday after Thanksgiving and runs through the end of year, is bigger. "[The delay] is going to affect Apple's appeal during the back-to-school season," Duboise said. "People will probably push back their purchases."

John Lynch, financial analyst for Needham & Co., agreed that Apple would see sales tip toward the latter part of the year. "I suspect that it's just going to be a time shift in their OS upgrade revenues," he said. "In addition to that, some customers may delay purchases of the Mac as well, but my suspicion is that won't be a particularly powerful phenomenon."

Apple, for example, could choose to hand out coupons similar to what Microsoft and computer makers did during the holiday shopping season. The coupons gave people upgrades to Vista at no additional cost when the OS was released in January. While many people waited anyway to buy new PCs, Lynch felt Apple would be more successful. "It's a lot less painful to upgrade the Mac OS than Windows."

Apple had originally been slated to launch Leopard in April, but decided to push it back to June to ensure that Macs running Leopard are also capable of running Vista.

In order to run both operating systems, Apple would have to finish work on a Leopard version of its Boot Camp technology, an Apple utility that enables Mac users to launch and run Windows. Boot Camp opens the Mac to running popular Windows software, making the computer a more viable option to people reluctant to switch from a PC.