Exelon Corp., the largest U.S. nuclear power operator, posted a 32 percent drop in quarterly profit Thursday as weaker margins from its power plants weighed, but it topped Wall Street expectations and raised its full year earnings forecast.

The owner of Pennsylvania’s PECO utility and Illinois’ ComEd utility posted second-quarter earnings of $445 million, or 67 cents per share, versus $657 million, or 99 cents per share, in the year-ago quarter.

Adjusted earnings were 99 cents per share, topping the 91 cents that analysts had on average forecast, according to Thomson Reuters I/B/E/S.

Revenue rose 6 percent to $4.40 billion.

Exelon raised its 2010 earnings forecast range to $3.80 per share to $4.10 per share, from $3.70 to $4.00.

Shares in the company were less than 1 percent higher in premarket trade at $42.