Ethnic separation has erupted throughout India's strategic northeast region, with armed insurrection in one state, threats of it in at least two others and nasty, sometimes violent demonstrations in Assam that have cut supplies of badly needed oil to the rest of the country.

The Indian Army has been put on alert to deal with escalating unrest in Assam, and a retaliatory weeklong blockade by Bengalis in nearby West Bengal has created scarcities of essential goods in Assam.

Although the Assamese demand that all "foreigners" -- including other Indians -- be ejected from their state currently holds the spotlight, the unrest there is symptomatic of the entire 100,000-square-mile region.

The situation is so unsettled in the northeast -- a parrot's beak extending into Burma and China and connected to the rest of the country by a thin "chicken neck" -- that the Indian government refuses to allow foreign correspondents to visit there.

"The whole northeast is in turmoil," said Laldenga, the chief of the Mizo National Front who lives here while out on bail on a charge of inciting rebellion in his native state of Mizoram.

Prime Minister Indira Gandhi said the unrest in Assam -- which has gone on for six months, has claimed at least 50 lives and has prevented parliamentary elections from being held last January in 12 constituencies there -- has now reached the point of threatening national unity and is causing "lasting harm" to India.

There were reports circulating here today that the state government is considering imposing preventive detention on the leaders of the Assam rebellion because of what is termed "secessonist tendencies."

While the action is taking place in one small, Colorado-sized area of the nation, its impact is felt throughout India.

Petroleum Minister Veerendra Patel, for example, said the closing of refineries and the crude oil pipeline in Assam has cost India -- which is already short of gas, oil and diesel fuel -- an extra $735 million over the past six months to import petroleum products.

More than anything, the Gandhi administration wants to restore the full operation of Assam's four refineries and restart the full flow of crude to a refinery in neighboring Bihar.

Clearly, though, any "quick fix" fashioned to settle the current Assam unrest is unlikely to tackle the underlying problem -- the Assamese feeling that their state is in danger of becoming dominated by "outsiders," many of whom have lived there for nearly 30 years.

The first influx of what Assamese call "foreigners" were Bengalis who started moving from what was then called East Pakistan, now Bangladesh, soon after the British rule ended in 1947. At that time they were considered refugees.

But the migration has continued, and has been joined by Bengalis moving from the Indian state of West Bengal in search of better job opportunities.

Although these Bengalis are clearly Indian citizens, they are regarded by Assamese foreigners.

"My party demands that each person staying in Assam must have two certificates of citizenship -- one for India and the other for Assam," said Assam National Party chief Girin Barua in an India Today interview.

While his statement may be political rhetoric, as Home Ministry Joint Secretary P. P. Srivastava asserts, there is no mistaking is popularity in Assam.

According to reports reaching here, the Assamese are united in believing they must expel as many as 5 million Bengalis who have settled there and who, they maintain, threaten the political and cultural survival of their state.

Assamese feel they only have to look to the neighboring states of Tripura and Sikkim, where natives there have been outnumbered by outsiders, for justification.

The current unrest started over the issue of who should be allowed to vote in last January's national parliamentary elections. The Assamese insisted the rolls be purged of all "foreigners" -- people who had come to Assam after 1951.

As a result of that dispute, the election still has not taken place in a dozen districts in Assam.

The Gandhi government has agreed to make the cutoff date for being allowed to stay in Assam 1971, but the All-Assam Student Association -- which has became the political power in the state -- insists the cutoff date should be 1951. Talks between the Gandhi government and the students have broken off.

The same fears of being taken over by outsiders dominate the other states in the northeast -- Mizoram, Nagaland, Meghalaya and Manipur.

"The movement in the whole northeast is a struggle for survival -- to preserve our identity and to keep from being submerged by other nationalities of India," said Laldenga.

The feelings of separatism are intensified by the northeast's physical and geographic isolation from the Indian heartland and by obvious cultural and ethnic differences.

The only land gateway to the northeast is a narrow "chicken neck" called Silguri, where members of Youth Congress-I from West Bengal mounted a retaliatory blockade last week to keep goods from moving into Assam.

Although the Youth Congress is a segment of Gandhi's ruling party, she has said there is little she can do to prevent the blockade. "You know," said the prime minister, "there is little you can do to control young people."

There is speculation in political circles here that Gandhi allowed the blockade to go on to create a breakdown of law and order in the Communist-controlled state of West Bengal so she could dissolve the government and call for new elections there as she did in nine other states.

These political machinations at the center add to the feelings of isolation in the northeast.

Moreover, the people look and act differently from most Indians. They are more akin to Chinese, Burmese or Tibetans. Laldenga and his family, for instance, look far more Asian than most Indians.

The entire region has been economically isolated from India. Assamese feel most of the good jobs have gone to Bengalis. In Manipur, another northeast state where a rebellion has been simmering for 15 years, people say they are used as a captive market for Indian products -- much the same cry that pervaded India's fight for in dependence from Great Britain.

The armed insurrections go up and down in these states. Currently, Nagaland is quiet. But there are reported to have been 18 deaths in battles with troops in Mizoram since January.

Srivastava, the Home Ministry secretary, said that Mizo and Naga nationalists are being supplied weapons and training by the Chinese and there have been reports of rebel camps over the border in burma.

There was also a statement in Parliament by Home Minister Zail Singh -- later denied -- that the CIA was involved in the unrest in the northeast. -Despite the Indian government's denial, it is widely believed here that foreign intelligence services -- the Chinese and Americans are mentioned most frequently -- are deeply involved in the Indian northeast.