Washington — ''We have made our proposals, the ball is now in the Sandinista court.'' So says Nicaraguan opposition leader Arturo Cruz, who says the opposition will not participate in November elections unless the ruling Sandinistas agree to hold a dialogue with the opposition. A dialogue, he says, would be a ''guarantee that both the election is carried out fairly and that its results are respected.''
July 25 and Aug. 4, the technical cutoff dates for registration to run in the election, have passed without the main opposition parties registering. But ''dates mean nothing,'' Mr. Cruz says. He says he is willing to participate in elections if the Sandinistas will agree to talk.
While each day that passes makes such an occurrence less likely, the opposition forces have made an important concession that removes at least one major stumbling block to a possible entente.
Cruz's original demand was for the Sandinistas to engage in a dialogue with leaders of all the opposition groups, including Adolfo Calero of the contra rebel forces in Honduras and Eden Pastora Gomez, who heads the anti-Sandinista forces in Costa Rica. However, this past week, the leaders of both armed groups removed themselves from the proposed dialogue in the ''interest of national reconciliation.''
The main opposition leaders decided that neither Cruz (whom the main parties named as their presidential candidate if they participate) nor Social Democratic leader Adan Fletes Valle (who was named as vice-presidential candidate) should participate in the talks since their feelings about running for office might impinge on their objectivity in negotiations. Therefore, the dialogue would be between the leaders of the ''Coordinadora'' - a coordinating committee of major opposition political parties and labor and business groups - and their Conservative Party allies on the one hand, and the Sandinistas on the other. Since there have been talks in the past between the Coordinadora and the Sandinistas, new talks would not be precedent-breaking or, in principle, particularly difficult for the Sandinistas to engage in.
The newest element, Cruz says, would be brought in by the opposition demand that a third party from another country be a witness to the talks and a guarantor of whatever written agreement would emerge from them. Cruz suggests that this witness could come from organizations such as the Organization of American States or the Socialist International.
The following points, a highly placed opposition source says, are the kind of guarantees that the dialogue would ensure:
1. Absolute liberty of press, including access to the news media.
2. Liberty of mobilization for the parties, including guarantees by the authorities that opposition rallies will be protected from attack by Sandinista turbas, or mobs.
3. Although the opposition does not dispute the right of soldiers to vote, it insists that voting urns should not be in barracks, government offices, or in Sandinista neighborhood block committees so that, according the opposition source, ''citizens can deposit their votes in complete secrecy without feelings of psychological pressure.''
4. The withdrawal of recent decrees stating that all distribution of the most basic foodstuffs will be done by the neighborhood block committees. The opposition wants guarantees that the Sandinistas will not exert pressure on opposition activists or voters by using food distribution, or the multitude of government licenses necessary in many activities in Nicaragua, as instruments of political pressure.
They also insist on assurances that the result of the elections will be respected. According to Cruz, the Sandinistas have said both privately and publicly that ''basic control of the country is not under discussion in these elections.'' For Cruz this is unacceptable.
The opposition believes that if it wins more than 50 percent of the vote, it should be allowed to take power, or that if it wins 30 or 35 deputies in the 90 -person Constituent Assembly, it should be allowed to take seats and have the kind of power due to important minorities.
Cruz's feeling is that in a pluralistic system minorities have rights.
''We will not accept from the Sandinistas what was unacceptable under (former Nicaraguan strong man Anastasio) Somoza, that is, to be governed by a regime of whim,'' he says. ''We do not want tolerance, we want rights. We want to know what are our rights within the political game; we do not want to live under the constant threat that today they are conceding us our rights and tomorrow they will take them away.''
Cruz believes that the Sandinistas' decision on whether to hold a dialogue will in part be governed by their feelings about whether they can risk holding truly free elections.
The opposition leader says that the kind of popular support he received on his recent trip to Nicaragua shows that a Sandinista victory is ''by no means certain.''
On Aug. 5, Cruz led an opposition rally in the provincial city of Chinandega. He says that the rally was attended by 8,000 to 12,000 people. Of that number, only 100 to 200 were bused in from outside the Chinandega area. A majority, he says, were neither middle nor upper class, but ordinary Nicaraguans. Cruz says, ''A large part of them were from the people, workers, peasants, young and old, all ages, all social levels.''
Cruz says that what surprised him especially was the numbers of people who came out of their houses and enthusiastically greeted him as the rally drove through the streets of Chinandega. Peopled even waved flags of the Sandinistas' political front, he says.
Cruz felt that the Sandinista reaction to this and other rallies was troubling to those who wanted to see free elections. Both in the northern town of Matagalpa on Aug. 4 and in Chinandega the next day, Cruz's supporters were attacked by Sandinista mobs. The night before the Chinandega rally, the platform he was to speak from was wrecked by what he alleges were Sandinistas.
Although the government says these were ''spontaneous'' manifestations of the feelings of the Nicaraguan people, Cruz doubts their spontaneity. He says that in any case the Sandinista police have a duty to stop them. In Chinandega, he says, it was the supporters of the opposition rally who beat back the mobs.
Cruz also questions Sandinista claims that the Nicaraguan people are united behind them.
''There is not one united Nicaraguan people, but two,'' he says. ''One part of the people pro-Sandinista and armed, and another part of the people against them and unarmed.''
The press's handling of the incidents in the two towns was also revealing, Cruz says. He alleges that the Sandinista-controlled TV news distorted the situation in Matagalpa and made it look as if Cruz's supporters had attacked the Sandinistas. And he says, when La Prensa, a newspaper that favors the opposition , carried front-page stories on the Chinandega rally, the government censored most of the front page. As a result, La Prensa decided not to publish that day. Cruz believes that the descriptions of poor people expressing support for the opposition proved too much for the Sandinistas to take.
Cruz also accuses some of the US press of distorting the nature of his campaign. In reporting that he never intended to participate in the elections, ''some of the press acted in an arbitrary and capricious way,'' Cruz says.
''We waited from July 25 to Aug. 4 for the (Sandinistas) to respond to our call for a dialogue. We asked for the electoral registration cutoff date to be prolonged in order for there to be more time in which a compromise solution with the Sandinistas could be worked out.''
The registration date was extended for 24 hours.