Two weeks after its debut, Radio Marti, the Reagan administration's controversial broadcasting service to Cuba, appears to be evolving into a surprisingly soft-sell propaganda operation with heavy doses of Spanish-accented news and music.

U.S. officials in Washington say they have no idea yet how the station is going over in Cuba, although it apparently can be heard without serious interference on the island. But they say they have rave reviews from the Cuban-American community in the United States and from others who applaud a program schedule that is clearly unfriendly to President Fidel Castro but lacks strident rhetoric.

In the view of U.S. officials, Radio Marti will have to log a lot more air time before any judgments can be made about whether it is effective in appealing to the Cuban people over the heads of Castro's state-controlled media.

But, in its short time on the air, the fledgling service has projected a different personality from what both its partisans and its critics had expected.

A sampling of its editorials and commentaries indicates that stringent efforts are being made to ensure the accuracy and impartiality of its news reports and to delineate them from editorial comment.

Similarly, its commentators speak in tones far softer than the acid-etched attacks on Castro that can be heard regularly on the half-dozen or so Spanish-language commercial radio stations that serve Miami-area Cuban exiles.

Instead, the Radio Marti editorials are Spanish translations of Voice of America editorials. In recent days, they have dealt with such topics as the superiority of free enterprise over state controls in helping Third World countries to achieve prosperity, explanations of U.S. policy on arms control and human rights, and criticism of the Soviet Union's suppression of organized religion.

The commentaries, done on a rotating basis by people known in the Spanish-speaking world for expertise in certain areas, deal more directly with Cuban affairs. The subjects covered on a typical day might involve shortcomings of the Cuban economy or the continued large-scale Cuban military presence in Angola.

But, while the commentator might argue that thousands of young Cubans are dying in a conflict that should not be Cuba's concern, he seeks to make his point through logic and facts rather than rhetorical broadsides.

In short, Radio Marti seems to be staking out a middle-road position among the various foreign-language broadcasting operations with which the U.S. government is directly or indirectly involved.

It has more punch and bite than the generally bland offerings of the Voice of America, where the emphasis is on presenting an upbeat picture of the United States. But so far it also has avoided the frequently strident and polemical approach of Radio Liberty, which broadcasts to the Soviet Union, and Radio Free Europe, which aims at the communist bloc countries of Eastern Europe.

That is because Radio Marti was created as a "hybrid" or "amalgam" of the two extremes.

The administration's original concept of Radio Marti in 1981 was that it would be a "surrogate broadcasting service", such as Radio Free Europe and Radio Liberty.

These operations, established covertly by the Central Intelligence Agency in the 1950s and now funded openly by the U.S. government, are intended to provide people in communist societies with information that they cannot obtain from their state-controlled domestic media.

Since Radio Marti was intended to fulfill the same function for Cuba, the administration initially wanted to put it under the control of the Board for International Broadcasting, a presidentially appointed independent organization that oversees Radio Free Europe and Radio Liberty.

That plan encountered strong opposition from congressional liberals fearful that extremist elements in the Cuban exile community would gain control of Radio Marti. To get the enabling legislation and funding from Congress, the administration had to compromise and put Radio Marti under the Voice of America, the broadcasting arm of the U.S. Information Agency.

Although Congress did grant Radio Marti some special leeway, the idea was that Voice of America supervision would provide more safeguards against ideological excesses.

Some of Radio Marti's original partisans expressed concern that this arrangement would result, as one put it, "in an operation that is neither fish nor fowl and that is so bland and innocuous as to have no impact."

However, that argument was disputed by VOA director-designate Gene Pell, who said in an interview, "The reactions we've heard in this country to the first few days of broadcasting have been almost uniformly laudatory.

"That includes the reaction from the Cuban-American community, which recognizes that stridency has no place in what we're trying to do and would be counterproductive in the long run."

The operating format worked out under Pell's direction for Radio Marti's 14 hours of daily broadcasting makes liberal use of techniques that the Voice of America and surrogate operations such as Radio Free Europe have found effective in attracting listeners.

Efforts are being made to appeal to different age groups with programs devoted to popular music, personal service features and sports. There is even a soap opera, a popular type of program in Latin America.

However, the backbone of Radio Marti's broadcasts is an emphasis on news. Pell, who has had a long career in commercial radio and television news, said he takes particular pride in "the accuracy, content and balance of our news report."

The news programs, which rely heavily on material supplied by the Voice of America's worldwide news-gathering resources, have a professional gloss that compares favorably with the programming of commercial stations throughout Latin America. The emphasis is on "hard news" coverage of daily events around the world. Samplings of its content over several days showed no signs of slanting or attempts to inject editorial comment.