SAN FRANCISCO - Apple is throwing out most of the real-world graphical cues from its iPhone and iPad software, like the casino-green "felt" of its Game Center app, in what it calls the biggest update since the iPhone's launch in 2007.

The new operating system, called iOS 7, strives for a clean, simple, translucent impression. Apple is redesigning all its applications and icons to conform to the new look, driven by longtime hardware design guru Jony Ive.

The operating system will show up on most iPhones, iPad and iPod Touches this fall, the company said.

The overhaul represents Ive's attempt to freshen the look of both the iPhone and iPad in hopes of deepening users' attachment to the trend-setting devices. It comes at a time when rivals such as Samsung Electronics and Google are trying to get people to defect by developing their own lines of elegant and often less expensive products.

The stiffer competition has slowed Apple's growth in the increasingly important mobile device market, contributing to a 38 percent decline in the company's stock price since the shares peaked at $705.07 in September.

Wall Street didn't seem nearly as impressed with Apple's new software approach as the sold-out audience of enthusiastic application developers who flocked to San Francisco Monday. Apple's stock dipped $2.92 to close Monday at $438.89.

The redesigned software uses simple graphical elements in neon and pastel colors. Gone is the effort to make the icons look like three-dimensional, embossed objects - a tactic known as "'skeuomorphism," that was favored by Apple's late CEO and co-founder Steve Jobs.

Interface designers call the new guiding principle "flat," but on the iPhone's main screen, the background image will move subtly with the movement of the device, creating an illusion of depth. Other screens include plenty of white space.

The software has "a whole new structure that is coherent and is applied across the entire system," Ive said in a recorded presentation. "The design recedes, and in doing so, elevates your content."

While the design modifications could help Apple distinguish its devices from rival phones and tablets, the company risks alienating longtime users.

"The new version is almost unrecognizable, which will make it polarizing," predicted Ovum analyst Jan Dawson. "Some people will love that their phone feels new and different, while others will be disoriented by the newness."

Raluca Budiu, a senior researcher specializing in usability at the Nielsen Norman Group, said the so-called "flat" design can confuse users, because it can offer fewer signals about where to tap or click. That's been the case, she said, with Windows 8, which has a very "flat" design.

What remains to be seen is whether Apple was fixing something that wasn't broken. Budiu noted that iOS users seem quite happy with the current iOS, which is easier to use than Google Inc.'s Android, its only big competitor.

Apple made a rare, major stumble with last year's iOS update, when it replaced Google's Maps application with its own navigation app. The underlying data for Apple's Maps was spottier and less accurate than Google's, users found. The Maps fracas didn't diminish the demand for iPhones, however.

Microsoft radical makeover of the Windows operating system in October provides a stronger example of the dangers of software revamps. Windows 8 was meant to give the company a stronger presence on tablet computers, but it ended up confusing many people who had become accustomed to using the old operating system on traditional desktops and laptops. Research firm IDC blamed Windows 8 for accelerating a decline in PC sales.

Among other changes, Apple's new iOS system will update apps automatically. It will store Web passwords online in Apple's syncing service, iCloud, making them available across devices. The AirDrop feature will allow sharing of big files with Apple-equipped people in the same room.

Apple took a jab at its rival, Samsung Electronics Co., which had been touting its Galaxy phones as better than iPhones because they sport near-field communication chips that allow people to share files by bumping phones together.

"No need to wander around the room bumping your phone with others," said Craig Federighi, senior vice president for software engineering.

The company also stepped up its rivalry with Google, maker of the Android software on Samsung and other phones. Apple said the Siri virtual assistant will use searches from Microsoft's Bing, Google's rival. Apple also is bringing its mapping service to desktops and laptops to compete with Google Maps and others.

Siri also is getting a new voice and becoming more versatile as part of the software upgrade. The program's robotic-sounding female voice will sound a little more human in iOS 7. For the first time since Siri's introduction in 2011, U.S. users will be given the option of having the assistant speak in a male voice. Siri will be able to perform more tasks, such as adjusting the brightness on a display screen, when asked.

The Cupertino, Calif., company is also launching a Pandora-like Internet radio service, iTunes Radio. It will be built into the Music app and stream music for free. There will be advertising, except for people who pay $25 a year for the iTunes Match online music storage.

Apple was a pioneer of online music sales and is still a leader in that field, but streaming services such as Pandora and Spotify have emerged as popular alternatives to buying. Pandora relies on its users being connected to the Internet at all times and plays songs at random within certain genres for free.

Last month, rival Google Inc. started an on-demand subscription music service called All Access that gives subscribers the ability to pick and choose specific songs and albums from a catalog of millions for playback on computers, tablets and smartphones in exchange for a monthly fee.

Apple updates its iOS operating system every year and doesn't charge for the updates. The new operating system will be available for the iPhone 4 and later models, and on the iPad 2 and later models, including the Mini. The launch of the new software traditionally coincides roughly with the launch of the year's new iPhone model.

Also at the conference, which runs through Friday, Apple revealed that it's switching from its more than decade-long practice of naming its Mac operating system updates after big cats. Instead, it's paying homage to the geography of its home state. Federighi says the next version of Mac OS X will be called Mavericks, after an undersea rock formation that produces big waves near Half Moon Bay, Calif.

The new operating system will extend battery life and shorten boot-up times, Federighi told the audience of software developers. The system improves support for multiple displays and imports the tab concept from Web browsers to the Finder file-organizer.

The software update will include iBooks for the first time, giving people who buy e-books from Apple a way to display them on the computer screen in addition to the iPhone and iPad. Competing e-book vendors such as Amazon and Barnes & Noble have cross-platform applications already.

There have been nine OS X versions named after big cats. The latest was Mountain Lion, released last year.

"We do not want to be the first software release in history to be delayed by a lack of cats," Federighi joked.

He said the new software will be out in the fall.

Apple also revealed a complete revamp of the Mac Pro, the boxy desktop model that's the work horse of graphics and film professionals. The new model is a black cylinder, one eighth the volume of the old box.

The current Mac Pro is the only Mac with internal hardware that can easily be modified and expanded by the user, but that possibility disappears with the new model. The company is adopting the same compact, one-piece design present in the Mac Mini and iMac.

The new Mac Pro will be the first Mac to be assembled in the U.S. in many years. CEO Tim Cook promised last year that the company would start a production line in the U.S., but didn't say where. Apple said the new computer will launch later this year.

Peter Svensson reported from New York.