Radio Marti, set up by the Reagan administration as a beacon of truth to Cuba, has become a flashback to the prerevolutionary 1950s for many bemused Havana listeners.

"It is as if somebody were giving us news from Eisenhower's time," smiled one middle-aged woman who said she has tuned in occasionally since the broadcasts began May 20 under the aegis of the Voice of America.

"The broadcasts are stagnant in time. The people they are speaking about are not known to the young people of Cuba," said another listener, who has lived here before and since the 1959 revolution. "They are the heroes of yesterday, not the heroes of today."

President Fidel Castro's government has denounced Radio Marti broadcasts to Cuba as "aggression." When they started two weeks ago, Castro retaliated by suspending a six-month-old immigration accord and threatened to take "additional measures regarding communications between the United States and Cuba."

This was interpreted as a warning of possible jamming of U.S. commercial stations, which Cuban officials have spoken about repeatedly since the idea of Radio Marti came up early in the Reagan administration as an antidote to Cuban censorship. No such steps have been taken, but Cuban and diplomatic sources said preparations are under way here in case Castro decides to put into practice a second threat, that of resuming medium-wave English-language broadcasts to the United States.

Cuban officials interviewed this week expressed particular offense at the facility's choice of Jose Marti for a name, since they associate the nation's 19th century independence leader with Castro's own efforts to assert independence from U.S. influence. Marti, a poet, was forced into exile in the United States, of which he once said: "I know the beast; I have lived in its entrails."

Some Havana residents, interviewed at random and without government officials present, scorned the new U.S. station for the name's sake.

"They don't have any sense of right and wrong, to use a name like that," fumed a 74-year-old retiree waiting for a bus.

"I think it is shameful," added Vivian Rosales, a cashier for an ice cream stand in a Havana park.

Tanya Gonzalez, a 21-year-old medical student at the University of Havana, said she has dismissed Radio Marti because in her view it can add nothing to information and entertainment she receives from Cuba's government-controlled radios.

"For music, we have our own music," she said. "For news, we also have our own news, and we prefer ours to theirs."

In private conversations with anonymity guaranteed, a number of Cubans said the new station's main drawbacks are that it sounds like a throwback to prerevolutionary days, ignoring changes Cubans have undergone since 1959, and that it purports to tell Cubans about Cuba without being able to do so.

"If only they could have some reporters here, because they have no idea what is going on," said an educated professional woman. "What can Radio Marti tell me? That I went to the store today and they didn't have soft drinks? I already know that, and they don't."

A Cuban journalist pointed out, for example, that a recent episode of the Radio Marti soap opera "Esmeralda" included a peasant whose wife died because he could not find a doctor for her. That could not happen in the Cuba of 1985, he added, because despite shortages in many areas the island has enough doctors in the countryside as well as the cities.

The professional woman said she was also surprised on the radio's first day of broadcasting to hear the voice of Miguel Portuondo Cala, a veteran sportscaster who left the island some time ago.

"He must be in his nineties," she said, chuckling. "I thought he passed away long ago. He was talking about baseball players nobody remembers."

She also expressed amusement at interviews and songs from Cuban emigre singers such as Celia Cruz and Olga Guillot, who she said have faded from the scene here, particularly among the half of Cuba's population that is under 40 years old and grew up under the Communist government.

"If you ask my opinion, I would say it is right out of the '50s," the woman added. "All these people still have the ideology and the outlook of the 1950s. It sounds as if the programs were taped 25 years ago."

The Cubans' comments, echoed by Latin American diplomats stationed here, focused on entertainment programs. But some officials expressed particular displeasure with news specials on the October 1983 Grenada invasion and the Cuban role in Angola.

A random sampling of news programs by a visiting American indicated emphasis on news from Angola, including communiques from South African-backed UNITA guerrillas claiming casualties among Cuban troops there. The edge on Angolan news also included an inaccuracy, attributing to Castro in a speech Wednesday a revelation that 25,000 Cuban troops are stationed in Angola. In fact, the Cuban leader stuck to his refusal to discuss precise numbers on the subject.

A number of Cubans, including some Foreign Ministry officials, expressed dismay that Radio Marti has erased regular Voice of America medium-wave news broadcasts. The VOA news was regarded as more trustworthy than the new programming, they said, because Radio Marti has from the beginning been seen as a project of Miami's hostile Cuban community, reflecting antipathy toward Castro and his government.

The new station's 14 1/2 hours of daily programming have been beamed to Cuba on 1180 kilohertz from the VOA's 50,000-watt AM transmitter at Marathon in the Florida keys, which previously was used for the VOA. As a result, VOA Spanish-language news broadcasts to Cuba on medium wave, which were widely listened to here, have gone off the air, remaining available only on shortwave broadcasts that cover all Latin America.