Rep. Christopher Murphy (D) expects to spend $10 million or more to capture the Connecticut Senate seat currently held by Sen. Joe Lieberman (I), who announced Wednesday that he would not seek re-election when his term expires in 2012.

“It’s going to be a very long campaign. It’s going to be expensive,” Murphy said in an afternoon conference call, speaking to the media for the first time since declaring his candidacy Thursday morning.

The 37-year-old Congressman, elected to his third House term less than three months ago, said he would have liked to have waited to launch a Senate bid, but “the scope and cost require you to start early.”

“It’s likely a race that will cost $10 million or more,” he said.

“I don’t have personal or family wealth,” Murphy added. “The process of building that large fundraising base requires an early entry.”

For perspective, recently elected Sen. Richard Blumenthal (D-Conn.) spent $8.7 million in his 2010 race, while his Republican opponent, Linda McMahon — who’s also said to be considering a run for Lieberman’s seat — spent just under $50 million.

Murphy said he had been considering a Senate bid for “the past several months” and had decided “in the past few weeks.” Asked whether he knew Lieberman was retiring, he did not answer directly but said, “I think it’s likely I would have run in either circumstance.”

He did not mention any of his likely opponents by name. Fellow Democrat and former Secretary of State Susan Bysiewicz formally entered the race earlier in the week. In doing so, she released an internal polling memo showing a 9-point lead in a head-to-head matchup against Murphy.

“I don’t know what the field for the Democratic or Republican nomination will look like. The prospective candidates had nothing to do with my decision,” he said. “There will be plenty of time to assess the field.”

Bysiewicz offered this statement:

“I welcome Congressman Murphy to the race. I look forward to a spirited discussion of the issues over the course of this campaign, focused on creating jobs right here in Connecticut.”

And facing reports that the GOP is eyeing Murphy’s 5th district seat as a pickup opportunity, Democratic Congressional Campaign Committee Executive Director Robby Mook offered a confident outlook.

“Democratic candidates for President won this district in 2000, 2004, and 2008,” Mook said. “Congressman Murphy handily won this seat three times, even in the difficult political environment last year. We are confident that we will win this overwhelmingly Democratic seat in 2012.”

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