By Rodrigo Campos

NEW YORK (Reuters) - Exxon Mobil on Friday reclaimed its place as the largest U.S. publicly-traded company by market value one year after losing it to Apple Inc, as shares of the tech giant extended their fall.

Apple's market capitalization has fallen by about $250 billion - roughly the market value of Google Inc - since hitting a high last September, when the stock traded above $700.

Apple shares traded down 2.6 percent on the day at $438.50, for a market value of roughly $411.8 billion. Exxon shares, up 0.2 percent on the day at $91.50, added to a market value of about $417.2 billion.

Apple "was clearly a momentum stock. Whenever the numbers behind momentum stocks stop, the momentum players are out and the stock tumbles," said Kim Forrest, senior equity research analyst, Fort Pitt Capital Group in Pittsburgh.

Apple shares slid 12.4 percent on Thursday - their biggest percentage drop since late September 2008 - as disappointing holiday-period iPhone sales reinforced fears it is losing its dominance in smartphones.

Apple shipped a record 47.8 million iPhones in the December quarter, up 29 percent from a year earlier. But that lagged the 50 million that analysts on average had projected.

"They make great products, expensive products, but as a value investor I'm interested in the unloved stocks, just not the recently-unloved ones," Forrest said.

Apple has finished the day as the largest company by market capitalization since the last week in January 2012, when it passed Exxon.

(Reporting by Rodrigo Campos; Editing by James Dalgleish, Gary Crosse and Sofina Mirza-Reid)