A passage in an article on Turkey in Sunday's editions was inadvertently changed to state that the nation could not govern itself. The writer had stated only that the Turkish military establishment had proven unable to govern competently.

Beset by monumental economic difficulties and terrifying internal violence from extremist militants of the left and right, Turkey teeters on the edge of chaos.

Political assassinations in Turkey average more than eight a day and increase month by month.

With martial law in 20 of the country's 27 provinces and the arrest this year of several hundred suspected terrorists, the government contends publicly that it was broken the back of the internal violence. Privately, however, the authorities are deeply worried.

They should be. The fact that they already have apprehended more suspected terrorists than their intelligence said existed is itself a mark of failure.

The increase in political murders this year has been dramatic. There were 119 in January, 147 in February, 153 in March, 201 in April and 202 in May.

The killings are the grisly work of political extremists, a proportionately small part of the population who, unlike the great majority, reject the nation's democratic institutions. Those of the left, virtually all Marxist, are avowedly revolutionary; those of the right have been simplistically anticommunist but may be moving toward a revolutionary goal as well.

Both sides have chosen violence as their weapons. They not only slaughter each other in what has become a kind of tit-for-tat blood feuding, but also others -- politicians, writers, businessmen, military officers and American soldiers.

The right-wing terrorists seem to be organized by elements of Alparslan Turkes' National Action Party. They are blindly nationalist, fascist or nearly so, and bent on the extermination of the Communists.

On the left there are well over 40 different organizations -- Leninist, Stalinist, Trotskyist, Maoist, Kurdish separatist, and Albanian (no less than three of these). It is hard to tell who is in charge.

The "brains" on both sides are younger members of university faculties and student militants. Themselves above the use of guns, they have as their troops the rootless, alienated young toughs of the slums.

It would be a comfort but also an illusion to hope that with economic improvement and less unemployment in Turkey the terrorism would end. It might well be lessened, but the roots of violence are far more political and social than economic.

The leftist students and academics are convinced that Turkish democracy serves only to protect and enhance the interest of the "haves." Discovering Marxim late -- Mustafa Kemal Ataturk had banned all communist literature and discussion -- they almost believe they invented it themselves. Beguiled by the feats of student agitation and violence in America and France of the 1960s, they dream that they too can come to determine the nation's future.

Gunmen for both sides are recruited from the gecekondus (literally, "settled by night"), large settlements around the principal cities, initially populated a decade ago by villages pushed off the land by population pressure (Turkey's population growth is a staggering 2.5 to 3 percent annually) and forced to search for work in urban areas.

More than half of Istanbul's inhabitants are in the gecekondus surrounding the central city. They are not the tarpaper and corrugated iron shacks of South American barrios nor the American Depressions's Hoovervilles, but rather consist of sturdily built houses with ramshackle gardens, essentially "village" in character and atmosphere.

The first settlers retained the stabilizing customs, family ties and conservative spirit of their rural communities. Not so their children, who reached adolescence about five years ago. They lack the behavioral anchors of their parents' villages, and they are also aliens to urban life.

Sensing themselves looked down on, ill at ease in their ambiguous surroundings, uncertain of their place and their identity, they are easy pickings for extremist recruiters who give them a sense of purpose and a feeling of importance.

Extremist ideology, although so far not much of the gunplay, has spread to factories and unions and, worse, to the police and armed services. Officers sometimes cannot trust their own subordinates, or noncoms each other in the same barracks, gendarmerie stations or guard houses.

Somehow the suspect in the murder of Abdi Ipekci, Turkey's finest newspaper editor and a thoughtful liberal, escaped prison through the connivance of his presumably rightist guards. Communist killers escape by the scores from other prisons.

In all this, the Soviet Union plays a large role. Its official diplomacy is respectful and it has granted Turkey large project loans on easy terms. Meanwhile, however, the Soviets continue to run guns and heavier weapons into Turkey from across the Black Sea, Soviet Armenia and Iraq. A youngster in eastern Turkey may not have enough money for bus fare but he will be carrying a Kalashnikov rifle.

The Palestine Liberation Organization, which equips and trains many left-wing gunmen in Turkey, is also presumably Soviet-financed. But the Soviets' most dangerous support is the large-scale aid it gives to militants among Turkey's Kurdish minority.

The Kurds, who number 7 million in a nation of 45 million people, have hated the Turks since the Seljuk conquest of their lands in the 11th century. hThere is considerable concern here that if Iran disintegrates, the Iranian Kurds would make common cause with their blood brothers in Iraq and eastern Turkey and try to form their own nation.

Eager to destabilize Turkey, the Soviets would surely support such a movement. Just as surely, Turkey would resist, and a war or something close to it would ensue. In such an event, it would be hard to see how NATO could remain uninvolved.

The Turkish military establishment would be as hard pressed to handle a Kurdish revolt as Ayatollah Ruhollah Khomeini has been to deal with Iran's Kurds. Despite the Turkish Army's size -- about half a million men under arms -- it is deplorably run down, working with inadequate and outdated equipment. It was devasted by the American arms embargo of 1974-78 and has not recovered since the embargo was lifted. In addition, the fight against terrorism has driven troops away from the training they should be getting.

What is needed is a large infusion of funds for new equipment. The difficulty is that the foreign aid that would allow its purchase must serve another, higher priority; the economic restoration of the country.

The United States has authorized military aid of $250 million for 1980 but may appropriate only about $200 million, and that in loans with interest at the American Government's own high borrowing rate.

An economically and politically bankrupt Turkey could, in theory, fall to the Soviet Union. That is unlikely, however, given Turkey's centuries of hatred and fear of the Russians. Only an outright military invasion could bring it about.

Moreover, the invasion of Afghanistan did wonders to concentrate the minds of the great majority of middle-of-the-road Turks. Occasional past flirtations with the Soviets and suggestions by politicians to look toward a new pro-Soviet accommodation are things of the past.

Equally unlikely would be Turkey's conversion to an Iranian-style Islamic theocratic despotism. Although the population is almost entirely Moslem, it is of the Sunni sect and relatively mild in its religious practices. Khomeini and his Shiites hold no appeal.

Much more probable in the event of a political collapse would be a Turkey turned neutralist, outside of NATO and looking to closer relationships with the Arab world for its security and a new role. Quite possibly it would be territorially fragmented, stripped of its small Arabic-speaking sector and its very large and strategically important Kurdish lands and people.

The resulting Turkish government could be a military one in a land which, for all its devotion to democratic principles in the past, has proved itself unable to govern under those principles or any other.

One can hear talk here, to be sure, of another military coup, such as that of 1960, which overthrew a right-wing tyranny. At that time, the Army devoted itself instantly to the restoration of a civilian government and accomplished it in three years.

But, having learned the difficulties of government the hard way, the older hands in the military have no stomach for trying it again. The chief of staff, Gen. Kenan Evren, is the personification of moderation and good sense on this score.

As the Turkish military establishment sees it, they have put all their eggs in the NATO security basket. The defense and economic cooperation agreement with the United States stands as a clear statement of Turkey's commitment. But what Turkey claims not to find is a matching commitment from the United States in the form of a real and meaningful military supply.The West Germans, in fact, may be making a rather better demonstration of their resolve than the Americans.

Bitterly, some Western Diplomats complain that the United States seems prepared to let Turkey get into military trouble but is not prepared to face the consequences.