Massive antigovernment unrest in India's strategic northeastern state of Assam for the past 10 months appears headed for a peaceful settlement giving Prime Minister Indira Gandhi her first major achievement since taking office in January.

In an agreement reached late Saturday night with the government, student leaders in the state called off demonstrations against immigrants into Assam. That agreement followed a cease-fire in the 14-year-old civil war in the neighboring union territory of Mizoram.

The demonstration in Assam had turned into the largest case of mass civil disobedience since the "Quit India" movement that lead to Indian independence from Britian in 1947.

The agreements in Mizoram and Assam were the first signs of a possible solution to mounting unrest in India's isolated northwest, a 100,000-square-mile region that juts into the neighboring nations of China, Burma, and Bhutan and Bangladesh and is connected to the heartland of India by a narrow neck.

The unrest, which also is included heavy fighting, posed one of the touchiest problems for the Gandhi government and carried with it the seeds of possible separatism. Moreover, the demonstrations in Assam have cut off its supply of vitally needed oil to the rest of India.

The major demand of demonstrators in the northeastern region has been the deportation of "foreigners," many of whom are actually Indians from other parts of the country while others have lived in the region for 30 years or more.

Despite the good omens from Assam and Mizoram, there are still signs of trouble in other parts of the region.

Unrest continues in Tripura, where tribesmen carrying machetes and bows and arrows rampaged through settlements of Bengali migrants in June and Massacred at least 1,000 in the worst bloodletting since independence. Police and Army raids have led to 600 arrests and the decovery of tiny arms factories hidden in the jungles.

The major issue is the same throughout the region, which feels isolated economically, culturally and linguistically from the rest of India.

Residents of the northeast feel threatened by "foreign" settlers, many of whom are Indians from the overcrowed neighboring state of West Bengal who have migrated to the region's five states and two union territories in search of plentiful, fertile land.

But there are also a large number of refugees -- perhaps as many as 5 million -- from Bangladesh who have been pouring across the border for more than three decades.

The deportation issue has not been settled in Assam. But the student leaders have called off a general strike, mass picketing and boycott on the shipment of all goods -- except the vital crude oil -- to the rest of India pending the start of negotiations on the problem later in the month.

It appears that the government will offer to deport all Bangladeshis who have entered Assam illegally during the past 10 years, while conferring alien status -- without citizenship or the right to vote -- on those who entered the state earlier.

There is little the government can do, however, about the demand to deport Bengalis who have migrated to Assam from elsewhere in India. Nor will it have an easy diplomatic task persuading Bangladesh to take back people who left that already overcrowed country during the past 10 years.

Even though there is a long way to go before the unrest in the northeast is fully settled, the prospect of a solution has provided one of the few bright rays in what many observers here regard as a dismal first eight months in office for Gandhi.

The crowning blow was the death in a plane crash six weeks ago of Sanjay Gandhi 33, the prime ministers' favorite son, political confidant and the heir apparent to the Nehru-Gandhi dynasty that has rulled India for most of its years as an independent nation.

The death came just after the mother-son team had solidified the ruling Congress-I For Indira) Party's grip on the country by winning eight of nine state assembly elections.

These victories were supposed to provide the support she needed to carry out her campaign promises to give India "a government that works," stem rampaging inflation, bring law and order to the country and end stagnation in industry growth.

The promises are still unfulfilled, and the loss of Sanjay Gandhi's iron fist on the party organization has allowed internal feuding to erupt among the Congress-I leadership in the states.

Furthermore, it has left the force of loyal young men whom Sanjay Gandhi injected into Indian politics foundering without a sponsor in the prime minister's court.

They are desperately seeking a substitute for Sanjay. One faction is pushing for his window, a 23-year-old Maneka Gandhi, while another wants his older brother Rajiv, 36, an Indian Airlines pilot, to become active in party work.

Maneka, editor of a magazine called Surva India, appears to have begun testing the political waters, although without any apparent support from her mother-in-law. Less than a month after her husband's June 23 death in the crash of a stunt plane he was flying, she appeared on television and on newspaper front pages planting trees in Sanjay's memory.More recently, she distributed food to the poor.

Despite these efforts, however, there are reliable reports that Rajiv Gandhi is ready to quit his job as a pilot to run for his brother's vacant seat in Parliament.

It appears unlikely, however, that introverted Rajiv will emerge as the tempestuous politicall leader that Sanjay had become. Nor, according to friends, will he be inclined to take Sanjay's youth movement under his wing.

The young followers of Sanjay form a solid bloc in the lower house of Parliament, and hundreds more were personally selected by Sanjay for state assembly seats.

"We feel orphaned without Sanjay Gandhi," said one of the youth leaders, Chunni Lal Verma.

More conservative and less impetuous than Sanjay, Rajiv is considered likely to gravitate to the old-line Congress stalwarts who had formed the base of his mother's support for years and who in many cases were displeased by his brother's young followers.