The tussle for capital on Wall Street — and for bipartisan agreement on Capitol Hill — has Constellation Energy Group scrambling to calm shareholders and employees who might be worried about prospects for completing its merger with Berkshire Hathaway.

For the second time this month, Constellation came out publicly to reassure its constituents that its business plans are on track, after a decline in its stock price and worries about its abilities to sustain during a down market.

“The defeat of the proposed federal bailout package in the House of Representatives sent markets reeling today, and stocks — including ours — continued to be buffeted by extraordinary pressure and volatility,” CEO Mayo Shattuck wrote in a memo to employees on Monday. “Fear and rumor are pervasive in this environment, and today we issued a joint statement to reemphasize that our merger with MidAmerican Energy Holdings Company remains on track.”

The statement “confirmed” that Constellation and MidAmerican, part of Warren Buffett’s Berkshire Hathaway, are still working on their merger documents for the Maryland Public Service Commission and the U.S. Securities and Exchange Commission. MidAmerican CEO Greg Abel said his company has “not identified any issues.” The deal had been announced soon after Lehman Brothers’ collapse earlier this month forced Constellation to look for buyers amid concerns about its liquidity.

Constellation had tried to assure shareholders previously, saying that the bankruptcy filing of Lehman, as one of its trading partners, would not materially affect Constellation’s business. It later did have an effect on the energy company’s ability to trade, however. Constellation in mid-September agreed to be bought by Berkshire Hathaway for an equity value of $4.7 billion, or $26.50 per share, a price that some observers considered a bargain.

Prompting this latest attempt to calm things, Constellation yesterday was facing rumors — carried by energy financing and trading site SparkSpread.com — that the company itself was preparing to file for bankruptcy as a contingency measure. Constellation’s shares fell by nearly 10 percent Monday afternoon. SparkSpread.com co-editor Victor Kremer noted to CFO.com that the story was not specifically denied by Constellation and MidAmerican in their joint statement.

However, Constellation spokesman Rob Gould says the company issued the news release to “reaffirm our position” following the story’s publication.

In his memo to employees, Shattuck asked that they hold tight as they wait for the financial crisis to settle. He said that he hopes that Congress will approve the $700-billion bailout plan for financial institutions, but that in the meantime, “the markets will continue to roil and stocks may experience dramatic swings. In this environment, it’s vital that we focus on the events we can control, and not lose sight of our business plans and commitment to safety and customer service.”