THE first round in President Reagan's undeclared war against the Sandinista government in Nicaragua foundered on the CIA mining of the approaches to Nicaraguan harbors. That act, illegal under international law (mining of international waterways is legal only during a declared war and then only after an enforceable blockade has been declared), produced sharp protests from the essential Western European allies and outrage in Congress, where Republican patriarch Barry Goldwater led the demand for an end to such behavior. The wave of disapproval brought legislation cutting off further United States military aid to the ``contra'' revolutionaries.
The undeclared war against Nicaragua had its genesis in 1981. Military activities funded and managed by the CIA reached their peak in early 1984. The mining of the harbors occurred during the first three months of that year. Then it all came tumbling down under a congressional rebellion.
Mr. Reagan let the matter rest for the balance of the election year. The contras in Nicaragua withdrew largely to their bases in nearby Honduras. There had been negligible fighting from then, until late July.
Mr. Reagan had bided his time until after this reelection, but he had not given up on his desire to do something to the Sandinista regime in Nicaragua. In February he began making speeches in which he called the Sandinistas communists, terrorists, aggressors, and stooges of the Russians. He began lobbying Congress to grant new aid to the contras.
In March he asked Congress again for more funds. In April a secret paper was sent to Congress proposing funding for a force of 20,000 to 25,000 contras for the northern side of Nicaragua and 5,000 to 10,000 more on the southern side. (Contents of the paper ``leaked.'')
In June the Congress finally gave in, in part. It agreed to provide $27 million in ``humanitarian aid,'' but stipulated that the funds could not be administered by the CIA or by the Pentagon. It left open a question about whom the task would go to.
Thanks to information that spilled out of Washington and Managua over the past two weeks we can now fill out the story.
The $27 million was not officially available to the contras until Mr. Reagan signed the bill on Aug. 8. But once its availability had been assured in June, new funds were available. Contra leaders spoke of ``fresh lines of credit'' having opened up.
We do not know where the extra funds were found for guns and ammunition. But it has been confirmed that retired US Gen. John K. Singlaub has been acting as principal US adviser to the contras and that he has been in regular contact with a person, unnamed, on the staff of the National Security Council at the White House.
It is confirmed at the White House that the National Security Council itself is dispensing the funds that Congress authorized for ``humanitarian aid.'' One report is that the Honduran Army has turned over to the contras US equipment left beind in US maneuvers in Honduras.
Presumably the newly equipped contra forces began, sometime in mid-July, to filter south from Honduras. By July 30 they were attacking the town of Estel'i, which is about halfway between the Honduran border and Managua, the capital of Nicaragua. On Aug. 2 they were attacking La Trinidad, another nearby town.
This is the deepest penetration yet by contras into Nicaragua. It was made possible by someone providing the contras with five DC-3 transport planes, famous from World War II. Airdrops from these five cargo planes have supplied the contras, who were last reported about 60 miles inside the country, but not yet in control of any sizable town or city.
But the Sandinistas had countered for the first time with Soviet MI-24 gunships, which they received during the recent lull in the fighting. The numbers of contras inside Nicaragua are now variously stated at 3,000 to 14,000.
One question is whether the contras will be able to stay inside for long with resupply from five ancient, and small, cargo planes. So far they have damaged two bridges, shelled a barracks, and killed perhaps a hundred Nicaraguan soldiers and civilians.
Another question is whether Congress, which specifically prohibited use of the $27 million for other than ``humanitarian purposes,'' will be satisfied with a distribution of those funds by the White House itself in a manner which, no matter how indirectly, has in fact permitted the reequipping of the contras with plenty of modern weapons.