After seven months of unchallenged prominence, Apple's hot-selling iPad now has its first credible competitor in the nascent market for multitouch consumertabletcomputers: the Samsung Galaxy Tab.

The Tab is being introduced over the next week by three major U.S. wireless phone carriers at $400 with a cellular data contract, or at $600 with cellular capability but no contract. The iPad starts at $499 for a Wi-Fi model with no cellular-data capability or contract, and is $629 for the least expensive model with cellular data capability but no contract.

Like the iPad, the Tab, which uses Google's Android operating system, is a good-looking slate with a vivid color screen that can handle many of the tasks typically performed on a laptop. These include email, social networking, Web browsing, photo viewing, and music and video playback. It also can run a wide variety of third-party apps. But it has major differences, most notably in size.

The Tab has a 7-inch screen versus the 9.7-inch display on the iPad. That may seem like a small difference, but the numbers are deceptive, because screen sizes are always described using diagonal measurements. In fact, the actualscreen real estate on the Tab is less than half of the iPad's. That's a disadvantage, but it allows the overall unit to be much smaller and lighter, and thus more easily used in one hand, something some users will welcome.

The new tablet will be introduced in coming days by Sprint, T-Mobile and Verizon, with a variety of cellular data plans. AT&Twill carry the Tab during the holiday season but hasn't announced its timing or data-plan pricing. Although it is being sold by cellular carriers, the Tab, like the iPad (which offers optional month-to-month cellular data through AT&T) can't make cellular voice calls.

I've been testing the Tab for a couple of weeks and I like it. It's a serious alternative to the iPad and one that will be preferred by some folks. It includes the three most-requested features missing in the iPad: a camera (two in fact); the ability to run Web videos and applications written in Adobe's Flash software; and multitasking, though, to be fair, the latter feature is coming to the iPad imminently via a software update. Another strong point is that like Apple, Samsung has rewritten some of the standard apps, such as the email and calendar programs, to make them look more like PC programs and less like smartphone apps.

On balance, however, I still prefer the iPad. For one thing, I like getting twice the screen size for a little more money up front -- as little as $29 for the no-contract model with cellular capability. For another, the iPad has vastly more apps specifically designed for a tablet versus a smartphone -- about 40,000 according to Apple, compared with a handful for the Tab. And it can run about triple the apps overall, if you count smartphone apps that aren't optimized for tablets.

Also, in my tests, the iPad's battery life was about five hours better than the Tab's, its maximumstoragecapacity is higher, and its aluminum body is more rugged than the Tab's plastic casing. Finally, the iPad can be bought in a Wi-Fi-only model that frees you from any entanglement with cellphone carriers. The Tab also has Wi-Fi, but, so far, no Wi-Fi-only version, though Samsung is promising one next year.

Still, the Tab is a very attractive product and I enjoyed using it. For buyers who want to spend less up front, don't mind the smaller screen, prefer the more compact dimensions and one-handed usability, and place high value on the cameras and on Flash, it may well be a better choice.

The Tab is a rectangular slate about two inches shorter and three inches narrower than the iPad. It is also a tad thinner. It weighs less than a pound, compared with 1.5 pounds for the iPad. While its screen is smaller, it has almost the same resolution as the iPad, so almost as much material can be displayed on it.

The screen is sharp and generally responsive to touch, though, in my tests, a bit slower than the iPad's screen. The Tab comes with 16 gigabytes of flash storage, the same as the base iPad. But with some carriers, this storage is internal and in others, it's on a removable memory card. The card slot comes on all models and can hold up to 32 gigabytes at extra cost. The iPad, also at extra cost, comes in versions that go up to 64 gigabytes, all internal.

With its lighter weight and smaller size, I found the Tab easy to use while standing and moving. It easily fit in one hand, though for many tasks you'll still need two hands.

Samsung and its partners make wildly varying battery claims for the Tab. The former says it can last up to 13 hours on a single charge, while T-Mobile claims just eight hours. I gave the Tab the same test I used for my iPad review: I put the screen on nearly full brightness, left the Wi-Fi on to collect email and played back-to-back videos until the unit died. My test Tab lasted six hours, 50 minutes, though at six hours, 10 minutes the screen dimmed irrevocably to a darkness level that made it useless. In the same test last spring, the iPad logged 11 hours, 28 minutes.

The Tab has a 3-megapixel rear camera with flash and a 1.3-megapixel front camera mainly for video calls. Still-photographs and videos I took were of average quality, but videos taken with the front camera were fuzzy.

I tested video calling using a pre-release, tablet-optimized version of Qik, the software being preinstalled for this purpose on the Tab. Results were mixed. It will work over either cellular or Wi-Fi connections, but the version I tried wasn't tuned for cellular, so we used Wi-Fi. In my conversation with a Qik executive, the call at first failed to go through. When it did go through, it worked fine for awhile, and then failed when I tried a feature designed to hide my image. Later, the audio dropped altogether. Qik says it is fixing the problems.