Managua, Nicaragua — A key spokesman for Salvadorean guerrillas says he is pessimistic about the chances for a negotiated settlement with the government any time soon. Ruben Zamora, a member of the guerrillas' political-diplomatic commission, argues that neither the Reagan administration nor El Salvador's government is showing a serious interest in negotiations.
At the same time, Mr. Zamora says that the leaders of the guerrilla movement are prepared to talk with President Reagan's special envoy, former Sen. Richard Stone (D) of Florida, whom the President recently appointed to facilitate a ''dialogue'' among the parties in the Central American conflict.
He added, however, ''We view the appointment in terms of American domestic politics. It's a reflection of the fact that the administration wanted $30 million more from the Congress in reprogrammed aid.''
The bearded, bespectacled Zamora is secretary-general of the Popular Social Christian Movement (MPCC), a group that broke away several years ago from the Christian Democratic group that was recently in power in El Salvador and which has continued to participate in elections there.
Zamora had served briefly as minister of the presidency in one Salvadorean government, following a young military officers' coup in October 1979. He became disillusioned with the American-backed government and resigned. Zamora's brother , Mario, also a Christian Democrat and at that time attourney-general, was assassinated by one of El Salvador's infamous death squads in February 1980. The Christian Democrats said that retired National Guard Maj. Roberto D'Aubuisson, now president of Salvadorean Constituent Assembly, was responsible.
In an interview, Zamora contended that if the US and Salvadorean governments were serious about a dialogue or negotiations, they would postpone elections now tentatively planned for November or December. -D'Aubuis son is expected to be a candidate for president.
But Zamora, who travels frequently to the US to lobby for guerrillas, admitted that the guerrillas made mistakes during the March 1982 elections in El Salvador. He said guerrilla leaders were now discussing what kind of tactics to use during the coming elections. The tactics would definitely be different this time, he said.
''I think we underestimated the desire for peace that exists among the people ,'' he said. ''We underestimated the power of propaganda during the elections. . . . I think we confused a lot of people instead of clarifying the issue for them.
''The policy was not to attack directly the electoral process,'' Zamora said. ''But at the same time, we said we are not going to stop the war just because of the elections.''
''What is quite clear is that the FMLN did not engage in actual disrupting of the elections, because the easiest thing to do would be to go after the candidate, and you don't need to shoot at them. You just go to them and tell them, 'If you are a candidate, we are going to shoot you,' and you can get at least 20 or 40 percent of the candidates quitting. But we didn't. Nobody was threatened. . . .''
Zamora acknowledged that in the 1982 election, there was ''a high turnout - no doubt,'' and in the next election the turnout might be equally high, ''although this time it is still to early to say.''
In the 1982 election, Zamora said, the government and the parties were saying: '' 'If you vote you are a democrat. If you don't vote you are a subversive.' And people know what happens to subversives or suspected subversives in El Salvador.''
Zamora also said that while the guerrillas could possibly win a military victory in El Salvador, ''The nearer we get to a military victory, the greater the danger of an all-out response from the Reagan administration. That means the participation of the Marines or something like that in El Salvador.''
The guerrillas could engage in a protracted war that would be less provocative to Reagan, said Zamora, but the ''problem with that alternative is what is going to happen to the country. . . . A protracted war destroys a lot. . . . And the cost of reconstructing the country would be incredibly high.''
Asked why the guerrillas engaged in economic sabotage, Zamora acknowledged that this activity carried with it ''danger'' because it might alienate the people.
''We are engaged in a sort of war that is irregular warfare,'' said Zamora. ''That means the basic principle is that the enemy is always more numerous, better armed, than our side. And in that sense it's a basic necessity of the war to maintain the enemy as much dispersed as possible.
You do this by making the enemy Army worry about bridges, about electrical facilities, about all the economy.''
Next: the guerrillas' war plans