* Mobile shopping on rise, Apple's iPad leads the way
* But many people spend less and buy fewer items online
* Shipping costs could eat into retailers' profits
By Jessica Wohl and Alistair Barr
CHICAGO/SAN FRANCISCO, Nov 24 (Reuters) - Next week's Cyber Monday should still be the top online shopping day of the year but it may pack less of a punch because online sales, a growing number involving mobile devices, soared on Thanksgiving and Black Friday.
Meanwhile, on Saturday, shoppers continued to visit stores though the burst that began on Thanksgiving night had subsided.
Black Friday, the day after Thanksgiving, had traditionally been the kickoff to the holiday season for stores. This year, retailers such as Walmart and Target made their biggest push ever with special offers during the holiday itself.
"The Thanksgiving creep revitalized the thrill for people," said Wendy Liebmann, chief executive of WSL Strategic Retail. "It got people excited to go out. But it pulled a lot of sales forward."
Cyber Monday, which follows the long holiday weekend, has been the biggest day for online shopping for many years, as workers return to their high-speed Internet connections at the office.
Now, armed with mobile devices, particularly iPads, shoppers are no longer waiting.
Online sales increased 17.4 percent on Thanksgiving Day and 20.7 percent on Black Friday compared to 2011, according to IBM Smarter Commerce, a unit of International Business Machines Corp that analyzes e-commerce transactions from 500 U.S. retailers.
Mobile shopping is more common than ever, with sales from mobile devices accounting for 16.3 percent of online sales on Black Friday, up from 9.8 percent in 2011 and 3.2 percent in 2010, according to IBM data.
Apple Inc's iPads and iPhones led the charge, with owners using the devices to browse and make purchases.
Mobile devices may have pushed more people to buy online, but shoppers did their homework. Many spent less and bought fewer items each time they clicked.
"We're seeing discounting along with free shipping really attracting some savvy shoppers," said Jay Henderson, strategy director for IBM Smarter Commerce.
The average order value on Black Friday declined by 4.7 percent to $181.22, and the average number of items per order dropped 12 percent to 5.6, IBM said.
Overall, the percentage of sales from online shopping is expected to rise. However, while retailers bring in more revenue from online shopping, they may also face some higher costs in terms of shipping a larger number of packages to more shoppers.
Among tablets, iPads were the clear leader, generating 88.3 percent of traffic to retailers' sites on Friday, followed by Barnes & Noble Inc's Nook with 3.1 percent, Amazon.com Inc's Kindle with 2.4 percent and the Samsung Galaxy with 1.8 percent, IBM said.
"It's either going to be a much bigger holiday or people are shopping earlier in the season," said Scot Wingo, chief executive of ChannelAdvisor, which helps merchants sell more on websites such as Amazon and eBay. "We won't know until later in the season."
Stores continued to use discounts to lure shoppers on Saturday, with Aeropostale Inc discounting items as much as 70 percent after a storewide 60-percent discount on Friday.
Rival American Eagle Outfitters Inc continued its two-day sale at 40-percent off, and Gap Inc's namesake chain was offering 60-percent discounts for the entire weekend.
"The discounts were reasonable but didn't take your breath away," said Liebmann. "Retailers are being cautious."
The real tests for retailers will be their levels of discounting over the entire season as well as the amount of online sales this weekend.
"American shoppers want to spend. Just give them a reason to come out," said Walter Stackow, portfolio manager with Manning & Napier. "They're trained to hold out for deals as Christmas gets closer."
The Garden State Plaza Mall in Paramus, New Jersey, appeared to be crowded on Saturday, though much quieter than on Black Friday, clerks at several stores said.
Some people were just starting their holiday shopping.
John Dunlap of East Orange, New Jersey, bought bedding at Macy's and said he skipped Black Friday as it is "too crazy" and not worth it unless someone is shopping for electronics. He said he would shop throughout the season only if he finds good deals.
"They have to give good discounts because of the economy," Dunlap said.
Vanessa Crenshaw, a 45-year-old accountant shopping at JC Penney, said that if stores pull back on discounts she'll go elsewhere.
"You can always find a deal, someone will have a deal," she said.