Nicaragua's Sandinista government has repeatedly violated the basic rights of Miskito Indians living there, including instances of "illegal killings" and torture, according to a report released yesterday by the Organization of American States (OAS).

The report, prepared by the OAS' human rights commission, also said that the ruling Sandinistas have used emergency military authority to "detain hundreds of Miskitos, without following legal formalities and without allowing any judicial remedy." It called on the government in Managua to thoroughly investigate documented abuses.

But while the report indicated continuing unconfirmed charges of rights violations, it said most serious violations took place between late 1981 and mid-1983. It added that "significant advances" have been made in improving human rights for the Miskitos since then.

The result of a two-year study, the document does not substantiate charges by anti-Sandinista Miskito rebel groups and the Reagan administration that the Nicaraguans have "implemented a policy of . . . ethnocide" against the 80,000-member Indian community.

The Inter-American Human Rights Commission of the OAS is charged with investigating allegations of rights abuse by OAS member nations. While its investigations are normally initiated by charges from nongovernmental sources, this one was initiated in February 1982 at the request of the Sandinistas. The request followed reports that they had abused and forcibly resettled the Indian community from its traditional homeland in eastern Nicaragua, near the Honduran border.

The Sandinistas subsequently asked the commission to facilitate a friendly resolution of their differences with the Miskito community. According to sources close to the commission, it was the failure of those efforts that led to release of the report.

Its publication yesterday coincided with the presence in Washington of Stedman Fagoth, head of MISURA, the largest of two anti-Sandinista Miskito guerrilla groups. Fagoth, whose Honduras-based group has launched a series of armed attacks against government forces in northeastern Nicaragua, is here to lobby for Congressional approval for continued CIA funding for his group.

The report noted that "the existing climate of conflict in the Honduran-Nicaraguan border region directly affects the observance of human rights." A source involved in commission deliberations said yesterday, "As long as tensions continue between the two countries, we don't see how the Miskitos' situation can improve."

After enduring centuries of abuse and neglect under the ousted pre-Sandinista government of Anastasio Somoza and his predecessors, the Miskitos' conflict with the Sandinista regime has catapulted them to world attention.

They are a people indigenous to the Caribbean Coast of Central America, who live primarily in small villages in Honduras and Nicaragua.

While most Nicaraguans are of mixed Spanish and Indian blood, Catholic and Spanish-speaking, the Miskitos were colonized by the English and evangelized by the Germans in the 19th century. An estimated 70 percent of them speak no Spanish, and most belong to the Protestant Moravian Church.

Hostility between the Miskitos and the Sandinistas, who came to power in 1979, was almost immediate, as the Sandinistas sought to impose nationwide land reform and collectivization of many sectors of the economy. The first outbreak of armed activity by anti-Sandinista guerrillas along the Atlantic Coast in 1981 created further upheaval.

It was during this period, in December 1981, that the most serious human-rights abuse documented by the commission report occurred.

According to the report, eyewitnesses said the Sandinista Army rounded up 35 to 40 Miskitos in the village of Leimus following an antigovernment rebel attack. The following day, they were taken out of jail in groups and "summarily executed."

While accounts of another, more recent killing were found to be untrue, the report said, other similar reports could neither be confirmed nor disproven.

Despite repeated urgings by the OAS commission, the report stated, two Sandinista military commanders identified as those responsible for the Leimus massacre were "totally and definitely acquitted" of the alleged crimes by a military court.

Beginning in 1982, to cut off rebel supplies, the Sandinista Army relocated the population of 42 primarily Miskito villages, setting the houses on fire and killing domestic animals. The OAS commission found that rebel military activity "demonstrates that there was a real and imminent threat to the security of the state," which could justify the forced relocation of 8,500 Miskitos to government-operated camps.

However, the report blamed the Sandinistas for the arbitrary fashion in which the "traumatic" relocation was carried out.

Fagoth and his supporters have said that "at least 393 Miskitos were killed" by the Army in the course of this exodus. The commission report mentions the death of 75 Miskito children in a helicopter crash during the relocation, but stated that no evidence could be found of other fatalities during this time.

Many Miskitos fled to Honduras to escape relocation or the armed conflict.

Today, 16,356 Miskitos live in refugee camps in Honduras, according to the United Nations High Commissioner for Refugees.