Radio Marti, the controversial White House initiative to "tell the truth to the Cuban people" via the airwaves, was to start broadcasting at 5:30 a.m. today without the fireworks that greeted its announcement almost four years ago.

"We confirm the initiation of broadcast of Radio Marti," the State Department said yesterday in a brief statement. The White House and State are to announce the broadcast in separate briefings today, the anniversary of Cuban independence.

Like Radio Free Europe and Radio Liberty in Eastern Europe, Radio Marti is intended to supplement the controlled news media in Cuba with news and cultural reports about Cuba and other countries, administration officials said. It will broadcast 14 1/2 hours a day and is named for Cuban independence leader Jose Marti.

"Jose Marti once wrote that a nation is not established the way a military encampment is run," President Reagan said in a videotape prepared for a banquet in Miami Saturday celebrating the anniversary of Cuban independence. "Today, the most prominent achievements of Fidel Castro's regime are the militarization of Cuban society and the propagation of malice and hatred."

The radio service has been transformed significantly since the White House conceived it in 1981 to report to Cubans "about their government's domestic mismanagement and its promotion of subversion and international terrorism."

In authorizing Radio Marti in 1983, Congress required that it operate under the Voice of America, which requires accuracy and a lack of bias in reporting the news. The legislation requires the service to be a "consistently reliable and authentic source of accurate, objective and comprehensive news," whose goal is "to promote the cause of freedom in Cuba."

Reaction to the start of Radio Marti broadcasts was muted yesterday, apparently because of the changes made by Congress in its charter.

"My own view is the more profoundly careful the reporting, the greater its effect will be in Cuba," Rep. Jim Leach (R-Iowa), who initially opposed the service, said. "I support Radio Marti as long as it is carefully done."

Cuban President Castro, who once threatened to retaliate against Radio Marti by interfering with internal U.S. radio broadcasts as far away as the Midwest, since has tempered his tone, calling radio interference a matter for bilateral discussions. His envoy here yesterday had no comment on the start of Radio Marti broadcasts.

The National Association of Broadcasters, which initially lobbied against the radio service because of fears of retaliation by Castro, yesterday voiced a wait-and-see attitude, along with continued concern about reprisals.

Critics continued to question how the service could provide objective news of Cuba. Officials confirmed it will have no correspondents there. An administration official close to Radio Marti said the news will be drawn from Cuban broadcasts, Cuban travelers, Cuban-Americans in contact with families in Cuba and elsewhere.

The start of the service has been delayed by ideological and bureaucratic struggles. It has filled only 127 of 178 authorized slots, an official said yesterday, and its first director resigned in January amid reported dissension between hardline ideologues and professional news staff.