RADIO MARTI is back: the Reagan administration's proposal for a new official station broadcasting just to Cuba--the Voice of America covers Latin America as a whole. At the time the proposal was derailed (mostly for extraneous considerations) last year, it seemed a good way to expand the listening choices of Cubans, as long as the broadcasts would serve the purposes of information, not destabilization. It still seems a good idea, but there's static on the line.

For some 15 years, Fidel Castro's prodigal domestic and international broadcasts, sent out without use of directional antennas, have interfered with domestic broadcasts in the United States and in the Caribbean and Central America. Notwithstanding widespread complaints, Cuba arrogantly announced new plans to expand greatly the power--and interference potential--of its transmitters.

In the Carter period, efforts were finally launched to work out a solution. But when Radio Marti was announced, the Cubans, seing it as hostile and provocative, rebuffed negotiations in the American- favored format. They have since ignored decisions of the regional body that allocates frequencies.

Fidel Castro is a practicing radio outlaw. But in his capacity to interfere with American stations, he wields a weapon for which the United States has yet to find a suitable defense. He threatens now to answer Radio Marti with more interference. During congressional hearings on the new radio, he brought his intent home to American broadcasters by jamming some 20 American commercial stations with the Voice of Cuba.

American stations, speaking through the National Association of Broadcasters, are aware that Cuba is using them in its fight against Radio Marti. They squirm in the role. But notwithstanding occasional mutters about "taking out" the offending Cuban transmitters, the American government has not done much about interference in the past. The record makes broadcasters wonder what help they will get if Radio Marti comes on the air.

Actually, American officials have taken some practical steps, agreeing, for instance, to have Radio Marti share the AM frequency already used for 20 years by the Voice of America. The Radio Marti legislation offers limited funds to compensate broadcasters for expenses incurred in mitigating Cuban interference.

The broadcasters did not create the conditions that make Cuban-American issues so hard to resolve. They are entitled to expect their legitimate commercial interests to be respected. Fortunately, patrons of Radio Marti, displeased by the NAB's effective lobbying, appear to be trying to meet the broadcasters halfway.