The human rights group Amnesty International has reported a "pattern of intimidation and harassment" of opponents of the Sandinista government in Nicaragua as well as abuses by the U.S.-supported rebels fighting to overthrow it.

In a detailed report released Tuesday on human rights in Nicaragua since the Sandinistas took power in July 1979, Amnesty said political, business and labor leaders sometimes are arrested, held incommunicado under harsh conditions and interrogated. Most have been released.

It said former prisoners reported being held in small cells with the lights on all the time, being threatened with indefinite imprisonment and being awakened every 10 minutes all night.

The report singled out for criticism the Interior Ministry's State Security Service, which it said routinely holds prisoners incommunicado and without charge under a state of emergency imposed in March 1982 as a response to attacks by the rebels, known as contras, or counterrevolutionaries.

Nicaraguan Ambassador Carlos Tunnermann denied that the opposition figures were detained because of their political activity.

"They were not arrested because they are civilian leaders but because they were helping to destabilize the country's economy, which is against the law, or preaching against the draft or cooperating with the counterrevolutionaries," Tunnermann said. He added that when the government learns of abuses it puts those responsible on trial.

The Amnesty International report repeated earlier criticism of the legal system created by the Sandinistas, particularly special tribunals set up in 1983 to try people accused of collaborating with the rebels.

The report also noted a "pattern of abuses" by the contras and said that it had received reports of "routine torture and summary execution of captives." It said the largest contra group, the Nicaraguan Democratic Force, known as FDN by its Spanish initials, was "frequently reported to retain no prisoners, killing captives on the spot or after brief field interrogations."

It added: "Witnesses of such killings have described in detailed testimonies made available to Amnesty International execution-style killings in which captives were bound, tortured and had their throats slit by FDN forces."

The report said that while Amnesty International condemns "the killing or torture of captives by anyone," it only takes action regarding governments because they are "bound by the international legal standards which Amnesty International seeks to uphold."

Last August, leaders of the rebel group said they had set up an internal organization to encourage its fighters to respect the rights of prisoners and civilians in the areas where they operate and to punish those who do not.

The report also took note of several unsolved killings and disappearances of persons detained by Sandinista forces in 1981 and 1982. It added, however, that in some recent cases members of the Nicaraguan police and military have been tried and sentenced for mistreating prisoners or civilians.

Another human rights group, Americas Watch, issued a report on Honduras, the nation to the north of Nicaragua where many of the anti-Sandinista rebels are based.

The report says the number of rights abuses in Honduras has decreased since the ouster of defense minister Gustavo Alvarez in March of 1984. It added, however, that there continue to be reports of torture, illegal detentions and the jailing of citizens "on shadowy or nonexistent charges."

The report charged that the Honduran military "is still responsible for the majority of human rights abuses in the country." It singled out for criticism the police and intelligence forces, considered part of the military, and noted that the Reagan administration has asked Congress to approve aid to the Honduran police.

The presence of thousands of U.S. troops in Honduras, on maneuvers designed to intimidate the Sandinistas, has had both beneficial and harmful effects on that Central American country, one of the poorest in the hemisphere, the report said.