A sonic boom, apparently from a U.S. spy plane, was heard over Managua today just as President-elect Daniel Ortega was telling 50 U.S. journalists that the Nicaraguan people were "getting angry" over the flights.

The sonic boom, heard at 9:25 a.m., was the third to be heard in three mornings. U.S. officials have acknowledged that sophisticated SR71 reconnaissance planes have caused earlier sonic booms here.

"Each day our people are getting more angry over the flights," Ortega was saying at a breakfast meeting with journalists just as the boom was heard. His stern expression remained unchanged at first, but he broke into a smile as the journalists laughed.

"How would the U.S. people respond if such a plane flew over their country each day?" Ortega then asked.

Ortega said that the country's armed forces were on maximum alert against a possible U.S. invasion.

[The Defense Ministry said in a communique issued later that military exercises, including training with explosives, would be staged every afternoon until Nov. 21, in an effort to prepare for the defense of the capital which it said would be one of the first targets of a U.S. invasion, Reuter reported.]