In a document that gives a rare insight into the problems of national minorities in Romania, a former high-level Romanian Communist Party official has alleged official repression against the country's 2 million Hungarians.

The claim is made by Karoly Kiraly, a member of the Romanian Communist Party Central Committee until resignation in 1975, in an open letter to the state and party leadership. A copy of the letter, which was written last month and smuggled out of Romania has reached Belgrade through usually reliable channel.

Kiraly, who is himself of Hungarian origin, alleges job discrimination against ethnic Hungarians and suppression of the Hungarian language in violation of Romai's constitution. Professing himself to be a loyal Marxist, he lays the blame not on the Communist system but on the Romanian party leadership and in particular the personality cult which surrounds President Nicolae Ceausescu.

Western diplomats in Bucharest consider the widespread, if muted, discontent among Romania's minority nationalities more significant than last year's short-lived human rights movement led by the writer Paul Goma, who is now in Paris. Support for Goma was confined to a handful of intellectuals, but national grievances run much deeper.

Last year, considerable disquiet was reported among ethnic Germans, Roma's second largest minority after the Hungarians, who were applying in large number to emigrate to West Germany.

There is, however, still no evidence that national unrest will have any effect on the policies pursued by Ceausescu. In his appeal, Kirali says that efforts to improve the lot of the Hungarian minority have brought no result.

Kiraly writes: "What mostly preoccupies me is the doggedness with which the problem is ignored by our party organizations from the grass roots to the highest level as something which does not exist."

A document attached to the Kiraly appeal, apprently prepared by his supporters abroad, states that he is now facing party disciplinary action for repeatedly calling attention to minority grievances.

In the letter, which is formally addressed to a Central Committee member for circulation among the party leadership, Kiraly alleges a wide gap between theory and practice in the treatment of the nationalities question. He cites cases of discrimination against the Hungarian minority in the mountainous region of Transylvannia in central Romania.

After recalling a promise for more secondary and technical schools with instruction in minority languages, he argues that the number of such schools is actually decreasing.

The use of the Hungarian language, Kiraly claims, is officially discouraged, even in the Nationality Council that represents the Hungarian minority. He claims that bilingual signboards put up during his term of office as first party secretary of Covasna County in 1971 have all been removed.

Alleging job discrimination against ethnic Hungarians, Kiraly writes that nearly all influential posts in towns with a Hungarian majority go to Romanians, many of whom do not speak a word of Hungarian.

Foreign observers familliar with minority problems in Romania find Kiraly's allegations plausible although it is difficult to confirm them. Western correspondents who visited the Jiu Valley last year, scene of Romania's worst post-war mining strike, were told that discontent among the sizable Hungarian minority there was an important factor in the unrest.

Miners explained that the area was once part of the Austro-Hungarian empire and was used to relatively higher living standards than the rest of Romania. They complained that Hungarian schools in the area had been closed down.

Romania's treatment of its largest national minority poses a delicate problem for its neighbor Hungary. The Hungarian government has no wish to pick a quarrel with a fellow communist state, but feels responsible for Hungarians outside the country.

While carefully avoiding any public protest, Hungarian officials frequently raise the problems of national minorities in Romania in private pilateral contacts.