MIAMI — As a taxpayer-funded radio and TV station run mostly by Cuban exiles expands broadcasts to Cuba in the wake of Fidel Castro’s ceding of power, they are also countering longtime critics who question their relevance, credibility, and reach.

Congress has approved roughly $500 million for both broadcasts since Radio Marti opened 21 years ago, and TV Marti five years later, in an effort to promote the free flow of ideas within Cuba. In addition to the stations’ annual budget of $27 million, Congress approved $10 million in 2006 to beam TV Marti into the island.

But many say it is a waste of tax dollars because the Cuban government jams much of the TV signal.

“They were told 16 years ago that to transmit a TV signal that far, it would be child’s play to block it out at the other end. It was child’s play, and it’s been blocked out,” Wayne Smith said. Mr. Smith was the head of the American Interests Section in Cuba to 1985 from 1979.

Because of the exiles’ involvement, Mr. Smith said, those on the communist island believe the station, named for the Cuban poet Jose Marti, has an anti-Castro bias. Many find it no more credible than the private Miami-based AM stations that reach the island he said.

A 1999 report by the State Department’s Office of the Inspector General found that the radio station failed to meet Voice of America broadcasting standards and lacked external oversight.

“It became just another exile radio station, and people in Cuba recognize that when they hear it,” Mr. Smith said of Radio Marti, which is produced by the U.S. Office of Cuba Broadcasting.

But an attorney and Bay of Pigs veteran who took over the office in 2003, Pedro Roig, said that in recent years it has revamped broadcasts to focus more on news and ensure programs are balanced.

“You’ve got to believe in the mission,” Mr. Roig said. “The point is to show debate, that democracy is people expressing their ideas without reprisal.”

On Saturday, TV Marti expanded its four-hour-a-night transmission to six days a week, using a new Lockheed Martin G1 aircraft to beat the jamming. The programming adds to weekly broadcasts transmitted since 2004 from an Air Force C-130 plane.

The new plane was unveiled days after an ailing Mr. Castro announced he was temporarily transferring power to his brother, Raul Castro.

Although anti-Castro messages remain the main dish for the stations, Mr. Roig said diverse viewpoints are encouraged.

“We have people who discuss the pros and cons of the U.S. embargo of Cuba, abortion, stem cells, so that they know there’s not one dogma,” he said.

The radio station transmits a mix of news from Cuba, America, and around the world. This week, the station has also been airing excerpts from a recently released presidential commission report on Cuba and urging Cubans not to take to the sea in rafts.

The most popular show, Mr. Roig said, is a sitcom called “The Chief’s Office,” a satire on life behind the scenes in the fictional office of a military leader with an extraordinary resemblance to Fidel Castro.

The Office of Cuba Broadcasting, which oversees both stations, holds focus groups with recent arrivals to find out what they want to see and hear. TV Marti now beams several youth-oriented shows with pop music videos but no overt political themes.

The broadcasts can be significant as long as they encourage change without sounding as if they encourage “meddling in Cuban affairs,” the executive director of the Cuban Study Group, a nonpartisan organization of business and community leaders, Tomas Bilbao, said.

“To the extent those messages are transmitted, it’s a great thing,” he said.

An independent survey by Intermedia Group pegged Radio Marti’s listenership at roughly 1 million, though station officials acknowledge it is difficult to get accurate information.