Nicaragua declares 'state of siege' after bridges bombed

Nicaraguan junta coordinator Daniel Ortega Saavedra announced a ''state of siege'' in Nicaragua March 15 after two key bridges had been blown up a day earlier near the Honduran border.

The immediate effects of the state of siege are censorship of papers and suspension of radio news programs. Only the official Voice of Nicaragua is allowed to broadcast news.

Nicaraguan leaders recently have complained that La Prensa, the chief opposition newspaper, and most of the privately owned radio stations have not been taking the ''military threat'' to Nicaragua seriously enough.

Recent stories in US newspapers that the Reagan administration is discussing formation of a paramilitary force to destabilize Nicaragua are taken seriously here.

The March 14 attacks on bridges spanning the Coco and Negro rivers follows a resurgence of sabotage attempts and attacks in border regions. The Negro River bridge, more than 200 feet long and just five miles from a key border crossing at El Guasaule, was totally destroyed. The Coco River bridge near Ocatal was damaged.

The Army chief for that border area, Manuel Salvatierra, said, ''these sabotages, for their professionalism, indicate they were carried out by well-trained elements.''

After Nicaragua's leftist Sandinista leaders ousted the dictatorship of Anastasio Somoza Debayle in 1979, Somoza followers sought refuge in Honduras and have been preparing for a return. In inteviews with this reporter last year, exofficers of Somoza's National Guard said they planned tocarry out sabotage and assaults in Nicaragua.

Besides the bridges, another major attack was the bombing of a Nicaraguan airliner. Nicaragua has linked ex-Somoza Guardsmen and separatist Indians to attacks in the northeast region; more than 100 Indians have been killed since December. A plot to blow up Nicaragua's only cement plant and only oil refinery was headed off in January.

Despite announcement of a state of siege, the atmosphere in Managua, the capital, is not particularly tense. Soldiers are not patrolling the streets. There is no curfew. Foreign journalists' reports are not censored. Marketplaces are still full of basic goods. Only sugar is rationed.

Orlando Tardecillas Espinosa, the Nicaraguan who surprised the US State Department in Washington by denying extensive Nicarguan involvement in El Salvador's civil war, arrived at the Managua airport to a hero's welcome March 15, greeted by thousands of young people.

Another traveler to the capital, new US Ambassador to Nicaragua Anthony Quainton, was not as warmly welcomed. At a press conference here he promised to work to ''better the difficult relations between the two nations.''

Nicaragua is just beginning a new militia training session. With current tensions, organizers hope for a big turnout. They are promising less marching, more combat training.