A planeload of U.S. humanitarian aid to the counterrevolutionaries, or contras, fighting the Nicaraguan government -- part of a $27 million package approved by Congress -- has been seized in Honduras and future shipments will be barred, the Honduran government said.

But contra leaders maintained yesterday that no aid had been confiscated.

And, both sides are right.

The incident illustrates the way veils of illusion tend to surround incidents in Central America that might otherwise upset the delicate structure of official myth about the aid.

Honduran armed forces chief of staff Gen. Walter Lopez Reyes said Wednesday that his troops seized the cargo of a chartered DC6 when it landed Oct. 10 at an airport near the Honduran capital of Tegucigalpa after a flight from New Orleans. To the Hondurans' surprise, American journalists were aboard.

Contra and diplomatic sources said the cargo was 14 tons of medicine and clothes intended for the rebels, who operate from camps in Honduras along the Nicaraguan border.

"Our country cannot under any circumstances allow this type of operation, which inflicts serious moral damage to the Honduran nation," Lopez said. "We cannot admit this cargo or allow others."

His statement reflected Honduras' longstanding position that it does not permit any Nicaraguan rebels in its territory. All sides pay formal respect to this official stand.

Adolfo Calero, leader of the Nicaraguan Democratic Force, the largest contra group, said at a news conference yesterday that one shipment of aid had reached his troops last week, and that a second plane, the DC6, had been stopped by Honduran authorities in Tegucigalpa.

But there was no indication anything had been unloaded, he said. "There has been no cargo seized by any government," he said.

This reflected the delicate position of the Unified Nicaraguan Opposition (UNO), made up of Calero's group and others, which needs and usually has the quiet cooperation of the Honduran government in moving supplies to its troops, as long as Honduras' official invisibility is maintained.

Honduran officials said last night that the cargo will be returned to the United States; Calero is understood to expect that it will be passed to him when the dust settles. But he cannot help Honduras to the point of acknowledging that there was a seizure, because he must also assure a vigilant Congress that not a nickel of the $27 million is being wasted.

Meanwhile, the State Department's Office of Nicaraguan Humanitarian Assistance was also on the spot, unable to discuss Honduras' allegedly nonexistent role.

"We turned all the aid over to UNO in New Orleans," a spokesman said. "The actual shipping arrangements were made by them." The State Department refused further comment.

Key to the mystery was the presence of NBC News correspondent James Miklaszewski and a film crew aboard the plane when it arrived in Tegucigalpa. As reconstructed by diplomatic and Nicaraguan sources, Honduran officials were surprised to see the journalists and seized the shipment in order to maintain their ability to deny involvement in the aid program.

Miklaszewski said in a report broadcast Monday night that the Honduran government is expected to take a cut from future shipments in return for allowing them to continue. Contra, State Department and Honduran officials all refused comment on that.