Air America, the progressive talk radio network, said Thursday that it would cease broadcasting immediately, bowing to what it called a “very difficult economic environment.”

“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 chairman of Air America Media, Charlie Kireker, said in a memorandum.

His statement was published on AirAmerica.com.

The news did not come as a complete surprise to staff members. The company, which was founded in 2004, never found a substantial audience or sound financial footing. It filed for bankruptcy protection in 2006, but managed to stay on the air at that time. The network churned through several owners and several attempted reinventions, with little to show for it.

“The fact of the matter was, it was always a very challenging business proposition, and it never had the right management,” said Sam Seder, who hosted programs on Air America until last year.

The headwinds were enormous, he said, adding, “Radio is a dying industry.”

Nonetheless, the network was a launchpad for a small number of liberal media stars, most notably Rachel Maddow, who now anchors a prime-time program on MSNBC.

Several former Air America hosts, including Randi Rhodes and Thom Hartman, remain on the radio but apart from the network. “It would be a shame if the world sees the failure of Air America as representing the failure of progressive talk radio,” said Michael Harrison, the editor of Talkers magazine.

Senator Al Franken, Democrat of Minnesota, hosted an Air America show from 2004 to 2007 before running for office.

In his statement, Mr. Kireker wrote:

At a critical time in our nation’s history — when dissent on issues such as the Iraq war were often denounced as “un-American” — Air America and its talented team helped millions of Americans remember the importance of compelling discussion about the most pivotal events and decisions of our generation. Through some 100 radio outlets nationwide, Air America helped build a new sense of purpose and determination among American progressives. With this revival, the progressive movement made major gains in the 2006 mid-term elections and, more recently, in the election of President Barack Obama and a strongly Democratic Congress. Laws have changed for the better thanks to this revival … but all the same our company cannot escape the laws of economics. So we intend a rapid, orderly closure over the next few days.

The shutdown of the network has essentially already taken place. Starting at 6 p.m. Eastern on Thursday, listeners will hear encore programming until Monday, “at which time Air America programming will end,” Mr. Kireker said in the statement.