A human rights organization that has sent four delegations of lawyers to Nicaragua said yesterday that the judicial system of the revolutionary Sandinista government there is politicized and permits some abuses of due process.

The report by the Lawyers Committee for International Human Rights also said the Reagan administration "shares substantial responsibility for the human rights violations that are occurring in Nicaragua today." It noted reports that U.S.-backed rebels fighting to overthrow the Sandinistas had committed "killings, beatings and violent harassment of unarmed civilian noncombatants." The Sandinistas have said the guerrilla war has forced them to abandon some traditional judicial safeguards.

The report was most critical of two special tribunals set up to try persons accused of participating in the insurgency. Each tribunal is made up of one lawyer and two lay people chosen because of their activism in Sandinista neighborhood groups.

The tribunals also do not follow strict rules of evidence, and there is no appeal to the regular court system, the report said.

Members of the four delegations the lawyers' committee sent to Nicaragua interviewed lawyers, human rights activists, judges -- including Supreme Court President Robert Arguello Hurtado -- and Interior Minister Tomas Borge.

The lawyers' committee report praised the regular judicial system for being relatively independent. It also said the Sandinista government had prosecuted police and soldiers accused of mistreating civilians and had allowed human rights groups to visit the country.

The report was critical of several other aspects of the judicial system in Nicaragua:

* Police can impose sentences of up to two years for certain offenses without trial in the regular courts.

* "Physical coercion" and occasional abuses against prisoners held by the Interior Ministry's state security section have been reported.

* Suspects in national security cases often are held incommunicado.

* The government sometimes has refused to honor court orders requiring the release of prisoners.

* Families of prisoners sometimes are not informed of their arrests.