Nicaragua's Sandinistas and their political opposition have tentatively reached an agreement for the opposition's participation in national elections, say sources close to this development.
The accord, say opposition figures and United States congressional sources, provides:
1. For Arturo Cruz Porras to run as the ''Coordinadora'' opposition group's presidential candidate in an election to be held in late January if rebels fighting the Sandinistas cease fire by Oct. 25.
The agreement would require both Honduran- and Costa Rican-based rebels to engage in the cease-fire. Postponing the election until January (the vote was to be Nov. 4) at least partially satisfies the opposition demands for more time to prepare for an election.
2. If there is no cease-fire, the election will be held Nov. 4 and Mr. Cruz will not participate. If the Coordinadora (an alliance of opposition political, labor and private-sector groups) has already registered Cruz as its candidate, Cruz will withdraw his name.
The tentative agreement was reached Monday night between Sandinista directorate member Bayardo Arce Castano and Cruz in Rio de Janeiro at a meeting of the Socialist International.
At time of writing, there was no official Sandinista confirmation of the accord, but Mr. Arce, a member of the ruling Sandinista directorate, presumably was empowered to negotiate a settlement in the government's behalf. The agreement is also subject to the approval of the Coordinadora, which is scheduled to meet next week.
The strength of the agreement also depends on whether rebel contra leaders Adolfo Calero and Eden Pastora Gomez follow through on pledges to cease fire if Cruz takes part in the elections.
Another factor is the position of the Reagan administration, which US congressional sources say exerts a strong influence over the Honduras-based contras and the more conservative wing of the Coordinadora. The administration probably could sabotage the agreement, if it wanted to, sources say. But it is seen as unlikely that the administration would take so hard-line a position.