Despite a White House plea for prompt approval of President Reagan's request for a radio station aimed at Cuba, legislative action on the $7.5 million authorization bill appears to have no chance of passage in the lame-duck session of Congress.

White House deputy press secretary Larry Speakes yesterday listed action on Radio Marti, named after Cuban patriot Jose Marti, as one of the pending legislative matters Reagan is most anxious to see acted on before the 97th Congress adjourns within two weeks.

However, Senate Majority Leader Howard H. Baker Jr. (R-Tenn.) said Monday that the bill appears to be stalled indefinitely because of controversies that have triggered a filibuster each time it has come up for consideration.

Conservative supporters of the idea, led by Sen. Jesse Helms (R-N.C.), say the station is needed to give the Cuban people more information about their country and the alleged determination of President Fidel Castro to support revolutionary activities in Central America and Africa.

However, the proposal is opposed by a coalition of midwestern senators, who say they fear Cuba will retaliate by jamming the domestic broadcasts of U.S. stations, and Democratic liberals, who contend that Radio Marti would exacerbate U.S-Cuban tensions.

A strong plea for the United States to go ahead with the station was made to Congress yesterday by Armando F. Valladares, a Cuban poet who came to this country in October after being imprisoned in his homeland for 22 years.

Valladares, speaking through an interpreter, testified before a joint session of two House subcommittees. When Rep. Jonathan B. Bingham (D-N.Y.) asked what the United States could do to promote change within Cuba, Valladares replied:

"At the present time, the United States could do the best service by giving the Cuban people access to information. That could lead to change. That is why I consider Radio Marti so important."

The hearing had been called to consider whether the tough line the United States has followed in dealing with Cuba for 20 years should be relaxed in favor of a more conciliatory approach.

But Valladares, who painted a grimly detailed picture of represion in Cuba, said the Cuban people have become disenchanted with communism, and said the United States should condemn Castro's imprisonment of dissenters and other human rights violations "in all possible forums."

He called the Castro regime "a dictatorship -- the most violent, the most ruthless known to mankind. It is maintained in power only by bayonets and a secret police that has under surveillance all the citizens of the island."

In other testimony, Thomas O. Enders, assistant secretary of state for inter-American affairs, assailed Cuba as "a would-be foreign policy giant ceaselessly projecting politico-military influence overseas and an economic dwarf which for years has shown itself incapable of providing material progress for its own people."

The administration, Enders made clear, plans to pursue its policies of keeping the economic embargo against Cuba in place and combatting what he charged is Cuba's aid to revolutionary insurgents in Central America and elsewhere.

But Wayne S. Smith, who resigned recently as head of the U.S. interests section in Havana because of disagreements with administration policy, charged that the administration's "confrontational approach has been, at best, unproductive; more often, distinctly counterproductive."