Air America, the six-year-old liberal-leaning radio network credited with helping the political career of Sen. Al Franken and discovering MSNBC prime-time host Rachel Maddow, announced Thursday it is ceasing operations immediately and plans to file for bankruptcy.

"It is with the greatest regret, on behalf of our Board, that we must announce that Air America Media is ceasing its live programming operations as of this afternoon, and that the Company will file soon under Chapter 7 of the Bankruptcy Code to carry out an orderly winding-down of the business," the network stated on its Web site Thursday.

The move represents a major blow to progressives, who had hoped that the 2004 launch of the network would counteract the radio dominance of right-wing personalities such as Rush Limbaugh and Michael Savage.

But the economics needed to make a 100-plus affiliate network work were simply not there, the network said in its statement.

The very difficult economic environment has had a significant impact on Air America's business. This past year has seen a "perfect storm" in the media industry generally. National and local advertising revenues have fallen drastically, causing many media companies nationwide to fold or seek bankruptcy protection.

The broadcaster cited the bankruptcy of Citadel Broadcasting last month ostensibly as proof that it wasn't its left-leaning outlook, but rather market conditions, that caused its financial problems. Citadel is the US's third-largest radio network.

At the time of its shuttering, Air America personalities included Ron Reagan, son of the late president, and long-time on-air personality Montel Williams.