MANAGUA, Nicaragua -- Nicaragua said U.S. spy planes Sunday broke the sound barrier twice over the country, causing minor damages and fueling the leftist Sandinista government's fears of an American invasion.
Within two hours of each other, what the Nicaraguans identified as a U.S. SR-71 'Blackbird' jets flew over Managua and other cities, breaking the sound barrier with a loud boom.
The spy planes, capable of flying at three times the speed of sound, flew over Nicaragua for the fourth consecutive day, causing alarm among residents and, apparently for the first time, minor damage.
Miriam Vargas called the Voice of Nicaragua to report that the explosion caused two walls of her Managua house, weakened by the 1972 earthquake, to collapse completely.
Cracks in buildings, fallen shutters and other similar damages were reported in Bocoa, Esteli and Leon.
'The famous Blackbird of the imperialists has again violated our airspace, our territorial sovereignty,' said the official Voice of Nicaragua radio in a special bulletin.
The latest overflights came amid reports that the Reagan administration was considering stepping up military and diplomatic pressure on Nicaragua in response to what it believes to be an accelerated arms buildup by the Sandinistas.
The New York Times said moves being considered by the administration included intercepting arms shipments at sea, recalling the U.S. ambassador to Nicaragua, larger and more frequent military maneuvers in Honduras and a resumption of aid to Nicaraguan rebels.
Secretary of State George Shultz, meanwhile, pressed U.S. concern over a Nicaraguan arms buildup in informal talks with Latin American foreign ministers gathered in the Brazilian capital of Brasilia for the Organization of American States annual meeting.
The confrontation between Washington and Managua -- their most serious since the Sandinistas overthrew dictator Anastasio Somoza in 1979 -- was triggered by the arrival Wednesday of a Soviet freighter that U.S. officials said might be carrying a cargo of MiG fighters.
No fighters were seen unloaded from the freighter Bakuriana in the Nicaraguan port of Corinto and Nicaraguan leaders insisted Washington was using the incident as a pretext for invading Nicaragua.
Two groups of Americans, numbering about 50 people each, organized anti-U.S. protests near Corinto. One group staged a sit-in, which they called a 'witness for peace,' near rebel-damaged oil tanks and said they would maintain a 24-hour-vigil to protest U.S. aggression against Nicaragua.
The second group, called 'Christians and Jews for Peace,' set sail Saturday in a fishing trawler to reach a U.S. frigate off the coast.
Upon reaching the ship, the group unfurled a banner reading, 'We pray for you and peace.' One reporter aboard the trawler said the frigate pulled away when the protesters were within a half-mile of it.
At high schools and other centers throughout Managua, some 20,000 students who were given a last-minute reprieve from harvesting the nation's coffee crop reported for military training.
At other locations in Managua, regular and reserve soldiers marched in formation and went through the rigors of training.
One air force regular said the armed forces were operating under a 'high state of combat readiness in wartime.'
The Defense Ministry said it would begin more than a week of special explosives tests in an isolated part of the capital. State media issued repeated bulletins warning people not to be alarmed.
The radio broadcast the tactical specifications of the sophisticated Blackbird spy plane and kept up its admonishments that the repeated flights signaled the countdown to a U.S. invasion of Nicaragua.
But despite habitual commotion caused by the sonic booms, the frequency of the flights also seemed to lessen their importance to some.
'When the spy plane goes over, we just look up and say 'adios,'' said one brigade commander at Managua's Jocote Dulce militia base.