UPDATE 3-Activist investors push Sempra Energy for strategic review, board shakeup

shakeup@ (Adds statement from Sempra in paragraphs 6-7, updates share movement)

June 11 (Reuters) - Two investors in U.S. utility Sempra Energy including activist hedge fund Elliott Management Corp on Monday urged a board shakeup and strategic review of the company's businesses, sending its shares surging as much as 18 percent.

Elliott Management and Bluescape Resources Co disclosed a combined stake of 4.9 percent in Sempra Energy and called the company highly undervalued, saying it could be worth an additional $11 billion to $16 billion or a share price of $139 to $158.

Sempra's shares were up 15.3 percent at $116.94 on Monday afternoon, off an earlier high at $119.72.

In a letter and a nearly 50-page presentation, the investors recommended that six new directors be added to Sempra Energy's board and said its conglomerate structure was made up of businesses that had "no compelling strategic or financial rationale."

They presented a plan for the company to pursue asset sales of its international business lines and split its existing business into two companies through a tax-free spinoff - one focused on utilities and the other on natural gas infrastructure.

Sempra said in a statement it is reviewing the investors' letter and presentation.

"Sempra energy is committed to an open dialog with all shareholders and considers investor perspectives in the context of the company's existing strategy and opportunities to deliver long-term shareholder value," the company said.

It was not the first time Elliott has partnered with Bluescape, a private investment fund founded by former utility executive John Wilder. They recently collaborated on two investments in the utility industry: NRG Energy Inc and FirstEnergy Corp.

New York-based Elliott Management, founded by Paul Singer, has $35 billion under management. Energy is one of its focus areas for investing.

Last August, San Diego, California-based Sempra, with backing from Elliott, bought power transmission company Oncor for $9.45 billion. Shares of California utilities have struggled in recent months as the state weighs a response to last year's wildfires, the largest in California's history, including whether to put the future burden of paying for wildfire damage onto power companies.

That could potentially cost California's main utilities, including Sempra unit San Diego Gas & Electric, billions of dollars each per year.

Earlier this month, the California Department of Forestry and Fire Protection, or CalFire, said a dozen of the wind-driven blazes that swept Northern Californias wine country last fall were sparked by power lines owned by Pacific Gas & Electric Co . (Reporting by Liana B. Baker in New York and Laharee Chatterjee in Bengaluru Additional reporting by David French in New York Editing by Meredith Mazzilli and Matthew Lewis)