Washington — The CIA-directed mining of Nicaraguan ports has stirred criticism even among exiled leaders of the anti-Sandinista opposition. ''While these actions are clearly an act of retribution, they nonetheless constitute a setback to the advancement of the democratic cause in Nicaragua and they weaken the moral authority of the opposition,'' says a top-level opposition leader, Arturo Cruz Porras.
A former member of the Sandinista ruling junta and former Nicaraguan ambassador to Washington, Mr. Cruz is widely mentioned as the most likely presidential candidate of the major Nicaraguan opposition party, the Conservative Party - if it decides to participate in the Sandinista-called elections in November.
Both pro- and anti-Sandinista Nicaraguans say the mining has come at a particularly delicate time. The Sandinistas and opposition leaders have been warily negotiating over conditions for opposition participation in the elections.
One well-placed Sandinista source says the mining has contributed to a general hardening of the Sandinistas' position - both in their stance toward the United States and internally, including the pre-election talks. As an example of the new, harder Sandinista line, this observer refers to Nicaraguan junta president Daniel Ortega Saavedra's call for international military help in opposing ''US aggression'' last March.
Cruz believes that what he calls the ''mistaken'' policy of mining the ports is playing into Sandinista hands. He says it permits the Sandinistas to claim that Nicaragua, and the countries whose ships are at risk, are the true victims, ''thus becoming winners in the eyes of international opinion and focusing attention away from their own excesses.''
Key Nicaraguan exile sources say that by committing an act that is clearly against international law, the US undercuts its own moral prestige and hurts the Nicaraguan opposition.
One moderate oppositionist states that the mining policy is part of a generally mistaken US policy of giving military aid to Nicaraguan counterrevolutionaries. The whole policy does more harm than good, he says.
In addition to any questions of morality, he says, the policy helps Nicaragua gain the support of Mexico, Venezuela, Western Europe, and the other countries. He says US policy would have been more effective had it sponsored a political campaign against the Sandinistas.
This observer believes that such a campaign - headed perhaps by Nicaraguan exile leader and former Sandinista war hero Eden Pastora Gomez - would cut off Nicaragua from vital international support.
Nicaragua government officials see the mining as further proof that the principal object of US support of the contra insurgents is the overthrow of the Nicaraguan government. They state that these acts show that the Reagan administration is not just interested in stopping the alleged flow of arms to El Salvador or in pushing the Sandinistas into negotiations.
Nicaragua's three largest ports - Corinto, Puerto Sandino, and El Bluff - are mined. According to Nicaraguan government sources, the most immediately felt economic effect has been to slow down importd of some key foods.
Oil imports, they add, have not yet been affected oil is delivered on large tankers that arrive only periodically. The Soviet ship that hit a mine in March carried oil, but it completed deliveries.
These Nicaraguan government sources say that exports have also been affected. Nicaragua is now harvesting cotton and coffee, its main export crops. These crops do not spoil quickly, but Nicaragua is starting to fall behind on its contracts for these products.
The same sources state that, while a majority of ships are still getting in and out of Nicaragua, a ''substantial portion'' are not. At least two international companies say they have stopped sailing to Nicaragua because of the mines.