Moderate political opponents of the Sandinista government today strongly condemned reported efforts by the United States to destabilize this country, although they labeled "excessive" the measures--including press censorship--taken by the Sandinistas in the face of the threat.

The Sandinistas, meanwhile, continued rounds of meetings with political and business leaders, as well as with the local and international media, in an attempt to explain why they have declared a "state of emergency" and what it is likely to mean.

Alfonso Robelo, a former member of the governing junta and now one of its prominent opponents, said, "We condemn all terrorist acts."

"When you see a ship in the Gulf of Fonseca , the U2s are flying overhead, then these bridges are blown up," said Robelo, "in order to be logical, you have to say there's a threat of aggression."

For the past several months, a U.S. naval destroyer has been stationed in the small Pacific gulf that separates Nicaragua and El Salvador. Last week, in an effort to prove that the Sandinistas, with Cuban assistance, have increased their military force to excessive levels, the State Department presented aerial surveillance photographs taken of Nicaragua.

Last Sunday, less than a week after reports in the U.S. press that President Reagan had approved a CIA plan of covert paramilitary action and economic sabotage in Nicaragua, the Sandinistas charged that two bridges had been blown up near their border with Honduras.

In Washington, the State Department said that the Justice Department is investigating claims by an anti-Sandinista exile group in Miami, the National Liberation Army, that it was responsible for the destruction of six bridges in Nicaragua, the Associated Press reported.

Robelo reiterated his belief that any attempt to overthrow the Sandinistas with violence or outside plots and interference would result instead in the destruction of moderate opponents and strengthen hard-liners within the current regime.

Alvaro Jerez, vice president of Robelo's party, the Nicaraguan Democratic Movement, succinctly expressed the feelings of the moderate opposition as its members watch the growing confrontation between this country of less than 2.5 million people and the United States: "The two locomotives are heading for a head-on collision, and we are just in the middle."

Robelo and other opposition leaders clearly believe there is a present danger, not only to the Sandinistas.

Jaime Chamorro, for instance, the publisher of the embattled opposition newspaper, La Prensa, said, "It's evident there is a campaign by the Reagan administration to prepare American public opinion for any possibility and they are probably aiding the counterrevolutionaries."

Robelo and other members of his party view the stories about the Reagan administration's destabilization plans, published last week in The Washington Post and The New York Times, as intentional leaks that are designed to destabilize the country in preparation for a possible invasion.

"Those articles are creating a tremendous problem here," said Robelo. "They are the beginning of everything." He proceeded to outline his fears of a destabilization plan that would include calculated leaks of information about covert support for "moderate opponents" of the Sandinistas after all other measures taken against the regime had made them dangerously nervous.

"When the moderates are all hanging in the streets of Managua, then the United States says look what the Sandinistas did to the moderates and use it as a pretext for an invasion," Robelo said. "We are cannon fodder."

During the three days since a bridge over the Negro River reportedly was destroyed and another over the Coco River badly damaged by saboteurs apparently crossing into Nicaragua from Honduras, the already tense atmosphere here has begun to crackle with perceived menace and conspiracy.

A military state of alert had already been in effect for the Sandinista armed forces for at least a week, but after the bombings a "state of emergency" was declared that suspended various constitutional guarantees, including freedom of the press.

Chamorro, whose newspaper has been shut down seven times by the Sandinistas since they took power in the July 1979 insurrection, said that he feels certain that "the principal objective [of the state of emergency] is to censor La Prensa and shut down the independent radio stations," which are required to transmit only the government emergency network.

The most conspicuous use of censorship to date was the closing of the pro-government newspaper, El Nuevo Diario, yesterday for one edition because of its banner headline calling the state of emergency a "state of siege," a term connoting harsh military rule.

In a press conference today, junta member Sergio Ramirez was careful to specify the differences, noting that at the moment there have been no political detentions, there is no curfew, there are no special military tribunals or blanket legal immunity for soldiers as is often the case in other countries under a state of siege.