The government has stepped up harassment of political opposition leaders and tightened press censorship in an increasingly tough policy against domestic dissent since national elections Nov. 4.

Officials have withheld exit visas in recent weeks for minor technical reasons from approximately 20 party leaders, businessmen and other opposition figures, mostly from the principal opposition group, the Democratic Coordinator alliance.

One government source acknowledged that an intimidation campaign was under way, and Sandinista officials warned that up to three opposition parties, all of them in the Coordinator, soon might lose certain organizing rights.

The left-wing Sandinista government has been punishing the Coordinator for boycotting the elections and embarrassing the government, according to opposition and government sources, diplomats and other political observers. The government also was unhappy when many opposition groups withdrew after the election from a national dialogue between the Sandinistas and dissenting parties and social organizations, the sources said.

The government apparently wishes to keep critics quiet and focus attention on rallying the nation to confront antigovernment guerrillas and what the government calls "Yankee aggression." A high-ranking government official commented, "The atmosphere is not good. I'm afraid that some of the opposition parties have become more radical and moved closer to the position of the counterrevolution."

The government's steps ended a three-month period during the electoral campaign when censorship was eased and some restrictions on parties were lifted. The steps have discouraged hopes for an early domestic political reconciliation following the election, and they appear likely to cost the government some support in public opinion abroad, the observers said.

Several prominent opposition leaders reaffirmed comments that U.S. government criticism and blustering against Nicaragua tended to make life more difficult for the opposition by fanning the Sandinistas' fears and strengthening hard-liners in the government here.

Outspoken government critic Enrique Bolanos, president of the opposition national business council, said, "It's true that with the U.S. attitude, the Sandinistas have more believable excuses" for repressing the opposition.

The Coordinator -- which includes the business council, four political parties and two anti-Sandinista unions -- boycotted the election because, it said, government restrictions prevented a fair contest. Six opposition parties outside the Coordinator ran candidates and together received one-third of the valid votes, with two-thirds going to the Sandinista Front. None of the opposition parties, which are small, has formal links with the antigovernment guerrillas, who were organized by and have received financing from the CIA.

Opposition leaders who have been prevented from leaving the country called themselves "The Captive Dissidents" in a statement released Thursday. Bolanos displayed photocopies of his passport to back his account of how an official at the airport tore out a page and then barred him from leaving the country on the ground that the passport was damaged.

Visa difficulties delayed but did not prevent trips abroad by Pedro Joaquin Chamorro, co-editor of the sole opposition daily newspaper, La Prensa, and Roman Catholic Bishop Pablo Antonio Vega, a prominent government critic.

Several opposition leaders said that the government was being malicious and petty over the visas, and even a Sandinista official called the harassment "foolish."

Censorship of La Prensa was up visibly in November from October, as the Interior Ministry barred about six articles a day, plus headlines and photograhs, in a typical week. Censored topics included Soviet Bloc arms shipments to Nicaragua, statements by antigovernment guerrilla leaders and the Interior Ministry's own censorship guidelines.

But some of the newspaper's feisty tone, evident during the campaign, still gets through. When former Venezuelan president Luis Herrera Campins visited here and reportedly urged the Sandinistas to promote pluralism, the afternoon daily's front-page headlines said, "Herrera Spoke Frankly." The two pro-Sandinista dailies in the morning had cited Herrera's visit as evidence of international support for Nicaragua.

In another sign of increased pressure on the opposition, the Social Christian Party's provincial president in Leon, Julio Montes, was arrested on charges of collaborating with antigovernment guerrillas, party and government officials said. The party also reported that a Managua provincial party official and her husband had been placed under house arrest for uncertain reasons.

The Social Christians broke with the Coordinator's other parties by continuing this month to participate in the national dialogue. The dialogue was suspended indefinitely Friday, however, with both sides accusing the other of intrasigence.

Previously the opposition parties participating in the dialogue -- mostly the ones that participated in the elections -- had hoped to use the discussions as a vehicle to press the Sandinistas for greater democratization. One factor in the apparent breakdown in the talks was the opposition's reluctance to endorse strong enough language to satisfy the Sandinistas in a proposed joint statement condemning the United States.

The government appeared to be uncertain about whether to crack down further on the opposition. The Social Democratic, Social Christian and Constitutional Liberal parties -- all in the Coordinator -- technically lost their "legal personality" when they boycotted the election. Now the government is considering whether to enforce the penalty, which would mean prohibiting public party meetings, closing party headquarters or adopting similar measures.

"We have a rightist sector in Nicaragua , which did not participate in elections, which is without rights," said Carlos Nunez, one of the nine commanders in the front's National Directorate and head of the Sandinista delegation to the newly elected constituent National Assembly.

But the full penalty of the law "has not been applied," Luis Rivas Leiva, president of the Coordinator and of the Social Democratic Party, said. If they lose their rights, party leaders say, they will move into the semitolerated underground where Nicaragua's opposition parties traditionally have flourished.

"In Nicaraguan political history, the parties hardly ever have had the right to a legal personality," Rivas Leiva said.