Edison Mission Energy, the little sibling of Southern California Edison, is growing up fast.

In the past six months it has picked up power plants in the Midwest, western Pennsylvania and Great Britain, more than doubling its assets. When those deals are finished, Edison Mission’s assets will reach $17.5 billion.

The company has 48 current projects in the U.S, Australia, Spain and the United Kingdom. And it’s building plants in Thailand, Italy, Turkey, Puerto Rico and Indonesia.

Altogether, Irvine-based Edison Mission Energy might be the world’s biggest independent generator of electricity. Its 30,000 megawatts of capacity are nearly 1 percent of the world’s total energy capacity. “That tells you something about our size,” said CEO and President Edward R. Muller.

With revenue expected to approach $3 billion this year, Edison Mission Energy would be one of Southern California’s larger public companies were it not a subsidiary of Rosemead-based Edison International (which is also the parent of Southern California Edison). Company-wide, Mission’s growing workforce is expected to reach 3,000 employees this year.

Edison Mission Energy began in 1986 as a subsidiary of Southern California Edison to purchase and develop energy-producing facilities. In anticipation of deregulation, it became a separate unit of SCE Corp., which later changed its name to Edison International.

With deregulation now in full swing in California and spreading across the country, utilities have increasingly been buying up power plants in areas outside their territories to diversify their revenue streams. Also, a growing number of independent companies have entered the potentially lucrative market.

Last year, 86 percent of Edison International’s total revenue came from its utility, while Edison Mission accounted for only 8.8 percent ($894 million) of its parent’s total.

However, Edison Mission contributes a sizeable slice to total profits nearly 20 percent of Edison’s $668 million in total 1998 net income.

Value Line analyst Arthur H. Medalie projects that Edison Mission Energy and mortgage lender Edison Capital will provide Edison International with half of its profits by 2001.

Muller said there are no plans to spin off Energy Mission. But the company appears to be positioning itself just in case, with a colorful annual report that looks like the kind public companies send to shareholders.

“There are people who believe that the sum of the parts might be worth more than the whole,” said Credit Suisse First Boston analyst Paul Patterson. “It has a proven track record in buying assets with great returns.”

Net income has increased steadily for five years, more than doubling from $55 million in 1994 to $132 million in 1998. “We’ve been targeting 15 percent to 20 percent growth in earnings and we have been beating that,” said Muller. He predicts a 20 percent to 25 percent increase this year.

There are an estimated 190 major independent power companies in the world. Some of Edison Mission’s main competitors are Virginia-based AES, an $11 billion asset company with power plants mostly outside the U.S.; EDF, the French government-owned utility that provides France’s power; and China Light & Power, the utility that supplies Hong Kong.

Many countries would like to attract the capital of Mission Energy. Muller said he has four major criteria when looking for places to invest.

“The first is the sense that the country is committed to private power,” he said. “Second, the country must have decent economic prospects. Third, there must be sufficient stability. And fourth, it honors the rule of law, particularly when it comes to contracts.”

Muller thinks deregulation across the United States is going well as a whole. But one place where Edison Mission has been conspicuously absent is California, a leader in electricity deregulation. Although the company has 11 mostly small plants in the state, Muller said, “it wouldn’t have looked good” if Edison Mission snapped up the plants that sibling Southern California Edison recently sold.

California began to deregulate its electric utility industry 14 months ago; the state is now in the midst of a four-year transition phase to full deregulation. So far, several hundred large power users, including major corporations and government agencies, have opted for different power providers. But smaller businesses and residents are largely choosing to remain with their utilities.

While two of the state’s three investor-owned utilities San Francisco-based PG & E; Corp. and San Diego-based Sempra Energy have been busy snapping up power customers both inside and outside their respective service territories, Edison has opted not to aggressively go after new power customers. Instead, it is diversifying into what it sees as more-profitable ventures, like the home security business and appliance service contracts.

Muller said Edison Mission might become more aggressive in California in the future, but has no pressing need to do so. “We’re confident that we can earn an adequate return for a good long time,” Muller said.