The State Department has concluded that the governments of three countries with long-standing military ties to the United States - Iran, South Korea and Nicaragua - continue to engage in widespread violations of human rights.

But, despite a 1976 law requiring such abuses to be considered in allocating military aid, only Nicaragua has been marked for a major cutback in military assistance under the Carter administration's 1979 foreign aid budget.

The human-rights evaluation are contained in still-secret reports made by the department on 105 countries receiving U.S. military, economic or development aid. These reports are required by the 1976 law to help Congress assess the administration's aid requests.

The 105 reports are scheduled to be made public later this week. However, The Washington Post has obtained copies of the reports on Iran, South Korea and Nicaragua - countries that have figured prominently in charges that the administration, despite its commitment to human rights, continues to support repressive regimes.

In all three countries, the reports note some improvement in the human-rights situation during 1977. In the main, though, they find that allegations of torture, cruel or inhuman punishment, arbitrary imprisonment and denial of fair trials still persist and, in many instances, "appear credible."

Yet, government sources admit, only Nicaragua - a tiny Central American republic that has been controlled for 42 years by the family of the current president, Anastasio Somoza - will be subjected to the pressure of a military aid squeeze in the fiscal 1979 foreign aid budget.

According to the sources, the proposed budget, which is expected to go to Congress later this month, will not cut off Nicaragua entirely. However, cating military aid, only Nicaragua has the request for Nicaragua will be lim-[TEXT OMITTED FROM SOURCE]

By Contrast, the sources said, South Korea, which is considered strategically important to American military interests in northern Asia, will continue to receive a high degress of military aid. The sources were unable to specify the exact amount that will be requested for 1979, but the administration earlier this year announced a $1.8 billion military aid program for South Korea to compensate for the planned withdrawal of U.S. ground forces there.

Iran presents a different problem because, as a country with enourmous oil riches, it does not receive military aid. But it is the largest singel purchaser of arms from the United States, accounting for $5.5 billion of the $11.3 billion in U.S. overseas weapons sales during the last fiscal year.

Because of Iran position as the world's second-largest exporter of crude oil and a major U.S. ally in the Middle East, the sources said, the administration has no plans to cut back on Iranian armes sales as a protest against the human-rights situation there.

In short, the correlation between the human-rights reports and the administration's military-assistance planning appears to underscore the complaint of rights activists that the administration's pressures are in direct relation to the size and importance of the country involved.

That complaint has been summed up frequently by the remark: "If you're the shah of Iran and have oil, you get treated differently than if you're the president of Nicaragua and have only bananas and sugar."

In the report on Iran, department analysts not that once-frequent charges of torture have declined significantly in recent months. They add that the department "does not believe torture has been used recently."

Also on the plus side, the report notes Iran's consultations with the International Red Cross on bettering prison conditions and says: "We believe the Iranian government is committed to prison reform and that prison conditions have indeed improved."

However, it also states that "cases of arbitrary arrest and imprisonment have occurred," that Iran still holds about 2,200 "state security" prisoners, that the militry and secret police still hold prisoners "for lengthy periods, sometimes incommunicado, without formal charging," and that, despite some recent improvements, persons tried on security offenses are handicapped by "important due process deficiencies."

In respect to South Korea, the department says it does "not believe that torture is now regularly employed." However, it cites allegations of political prisoners being beaten and held in solitary confinement and of continued arrests, detentions and searches without warrants under the Korean regime's "emergency measures" powers.

"As of late 1977, we estimate that fewer than 150 persons remained in prison under Korean emergency measures," the report says.

"At the heart of the human-rights problems in Korea is the restriction of political liberties," the report says. It adds, though, that since early 1977 the regime has tried to avoid using show trials and arrests against its political foes, relying instead on stepped-up surveillance pressures.

The Nicaragua report cites "a few reports of torture or beating of prisoners in 1977" and accusations of murder, rape and other mistreatment carried out by the National Guard against rural peasants as part of Somoza's campaign against leftist guerillas.

It says the Catholic order of Capuchins reporteed 55 deaths or disappearances as recently as January, 1977. But, it adds, no similar reports have been received since last February and "the number of reported abuses and their severity have decreased markedly over the past year."

The report gives much of the credit for improvements during 1977 to Somoza's lifting of a long-standing state of siege - a move that restored a large measure of press freedom and reinstituted public trial by jury for most prisoners.

The report also expresses concern that these improvements might be set back by reactions to the violence and unheavals in Nicaragua since the murder last month of opposition leader Pedro Joaquin Chamorro. The report was completed before most of the current trouble began and the State Department yesterday issued a formal statement calling for an end to violence in Nicaragua.

Most of the charges cited in the three reports are not new. In most cases, the reports state specifically that they are noting allegations already raised by such human-rights watchdog organizations as Amnesty International - sometimes without additional comment and sometimes with the department's observations about whether the charges appear credible.

But the repeating of these charges in reports bearing the official imprint of the U.S. government is expected to trigger charges from many of the countries covered about improper U.S. interference in their internal affairs.

Last year, for example, six Latin American countries - Brazil, Argentina, Chile, Uruguay, El Salvador and Guatemala - rejected all or part of U.S. aid because of Washington's criticism of their human-rights situations.

The expectation of further angry responses to the new reports has caused some rights activists to question whether the State Department may have toned down some of the reports to avoid trouble with allied governments. However, sources in the department's Bureau of Human Rights said they are satisfied that the reports on individual countries represent, in each case, an impartial assessment of the situation based on all the available evidence.