THE SANDINISTAS claim the crisis in Nicaragua arises from their conflict with the United States. This is not so. It arises in the first instance from their conflict with their fellow citizens, especially with the democratic people who fought the Somoza dictatorship, whose leaders served the Sandinistas in the early period and who turned against the Sandinistas only when they found the democratic promise of the revolution being denied. This needs to be understood in order to see the importance of the offer the democrats have just made to the Managua regime.

The offer comes from a newly, finally unified group including the political opposition led by Arturo Cruz and major branches of the armed resistance. Its essence is a proposal for a unilateral cease-fire by the contas to be followed by a political dialogue presided over by the bishops. The proposal is, in our view, entirely fair and reasonable. The Sandinistas protest the war? Here is an offer to stop it. How must they pay? Only by joining a process that points to the original goals of their own revolution. Their own man, Daniel Ortega, can remain president as the process unfolds. The proposal offers more than a chance for national reconciliation. It lets Nicaraguans remove their fate from foreign hands and restore it to Nicaraguan hands alone.

The Sandinistas' initial response to the proposal was to bar Arturo Cruz from returning to Nicaragua to announce it and to summon some of its local supporters to state security headquarters on grounds that they were participating in a U.S.- sponsored plot to overthrow the Sandinista government. Think of it: An offer by the opposition to put down arms and to start talking about achieving the Sandinistas' own early promises is dismissed as a hostile conspiracy.

How do the Sandinistas intend to explain to the Nicaraguan people a refusal to enter a dialogue on such a reasonable basis? How can any other independent-minded Latin country -- must that exclude Cuba? -- fail to support this proposal? In El Salvador, the government accepted a dialogue without even getting a cease-fire in return. The government in Nicaragua is being offered a better deal. Perhaps it will think again before delivering a final rejection.

And -- the inevitable question -- if the rejection is final? No doubt some will argue that the Sandinistas' failure to take the offer seriously makes American support of the contras unarguable. The drafters of the Nicaraguan opposition proposal, however, are shying away from that claim. Desperately, they are making a "last effort to grant to our country a civilized solution."