* China seeks WTO backing to impose sanctions on U.S.
* Apple gains ahead of expected new iPhone launches
* Energy stocks gain along with crude oil prices
* Western Digital, Seagate, drop on NAND price worries
* Indexes up: Dow 0.57 pct, S&P 0.45 pct, Nasdaq 0.58 pct (Adds quote, updates to early afternoon)
By Shreyashi Sanyal
Sept 11 (Reuters) - U.S. stocks powered higher on Tuesday, shaking off a subdued start, as Apple led a jump in technology stocks and a rise in oil prices lifted energy companies.
Apple rose 2.4 percent, boosting the three major indexes, a day ahead of an highly anticipated event in which the company is expected to unveil new iPhone models.
The technology sector rose 0.82 percent, on pace for its biggest jump in two weeks, also boosted by Microsoft and Facebook, which were up about 1.5 percent.
"Technology stocks are rallying with some positive catalysts like the Apple event coming up," said Cliff Hodge, director of investments at Cornerstone Wealth in Charlotte North Carolina.
"The sectors which have been the natural leaders, like tech, are catching a bid this morning, with some lift from energy stocks that will help buoy the markets."
The energy index was up 1.27 percent, the most among the 11 major S&P sectors, as oil prices rose after U.S. sanctions squeezed Iranian crude exports and tightened global supply.
Still trade tensions continued to linger after China told the World Trade Organization it wanted to impose sanctions on the United States for its non-compliance with a ruling in a dispute over U.S. dumping duties.
President Donald Trump had on Friday threatened to slap tariffs on nearly all Chinese imports.
At 13:07 a.m. ET the Dow Jones Industrial Average was up 146.87 points, or 0.57 percent, at 26,003.94, the S&P 500 was up 13.00 points, or 0.45 percent, at 2,890.13 and the Nasdaq Composite was up 46.13 points, or 0.58 percent, at 7,970.29.
Eight of the 11 major S&P sectors were higher. The biggest decliner was the utilities sector, down 0.39 percent.
Also enjoying gains were shares of companies that could see a boost in sales in the aftermath of Hurricane Florence, which was upgraded to Category 4 ahead of landfall on Friday.
Home improvement retailers Home Depot and Lowe's rose about 1.5 percent. Generator maker Generac was up 1.9 percent, while shares of construction material companies rose between 0.95 percent to 2.1 percent.
Activision Blizzard jumped 6.3 percent, the most on the S&P, and Take-Two Interactive gained 3.8 percent after brokerage Stifel forecast a strong reception for their videogames in the holiday period.
Western Digital slid 3.6 percent after RBC echoed other brokerages in warning that falling NAND chip prices would hit the company. Rival Seagate dropped 2.4 percent and chipmaker Micron 3.5 percent.
Advancing issues outnumbered decliners by a 1.30-to-1 ratio on the NYSE and a 1.01-to-1 ratio on the Nasdaq.
The S&P index recorded 35 new 52-week highs and 14 new lows, while the Nasdaq recorded 85 new highs and 81 new lows. (Reporting by Shreyashi Sanyal in Bengaluru; Editing by Arun Koyyur)