This year is a 10th anniversary for Lebanon, but let's not raise a glass. For 10 years, with barely a lapse, the Lebanese have been killing one another. We can conclude, from their unrelenting barbarity, that occasions to toast the war still await us, perhaps years hence.

What is apparent is that Lebanese have learned little -- about living together or living apart. They might have remodeled their government, long dominated by Maronite Christians, to broaden the political base. Or they might have fashioned a federated state to permit their diverse communities to live as neighbors with a minimum of a daily contact. Instead, they continue to kill.

Now the world is bored with Lebanon. Ho-hum, another car bombing, 50 dead. Another shell into an apartment building, 20 killed, worth a paragraph in the back pages of the newspaper. How many times can someone watch human annihilation on the television screen without growing numb to it?

It is not just Westerners who are callous. Indifference also pervades the Arabs, kin to the victims. Arab writers and intellectuals yawn over Lebanon. In Damascus and Riyadh, the tragedy long ago stopped being dinner table conversation. Lebanon is a show that has run too long.

Last month, the TWA hijacking focused attention once again on the Lebanese arena. But no one saw the country. The camera turned on innocents, victimized by a band of outlaws. Washington, least of all, cared about understanding the hijacking as the symptom of an agonizing and complex political problem.

The victims were American because many Lebanese see the United States as deeply involved in their affairs. They find it convenient to blame others for their own madness, if not Americans, then Palestinians, Syrians, Israelis. Shifting the blame helps the Lebanese retain their own sanity.

Why, they ask, does America, the most powerful and bountiful of nations, not come to our rescue, as Eisenhower did in 1958? Why does it help only the Zionists? Lebanese, who are by no means outlaws, and who were ashamed of the murder on the plane, hoped the hijacking would somehow transmit a desperate cry.

The Reagan administration was icy cold. It talked of retaliatory bombing, which would leave the hijackers untouched, and a blockade of the Beirut airport, which can only exacerbate the wounds of the most unfortunate. For the moment, Washington seems to have shelved the idea of retaliation, and the Syrians are working with a Lebanese committee to improve airport security. But few believe the situation will in any way change.

Long forgotten is the joy that greeted President Reagan's decision in 1983 to send in Marines to promote peace. The United States, Reagan said, had "vital interests" in Lebanon, but his policy was to support the Maronite- dominated "legitimate" government. Failing to condition his suport on expansion of the power base, he only aggravated the situation that gave rise to the civil war in the first place.

The opportunity ended when 265 Marines were killed in a bombing by unidentified terrorists, believed to be Shiites. Despite our "vital interests," the president withdrew the Marines, handing terrorism a clear victory. More important, he waived what may have been Lebanon's last chance for salvation.

In fact, what 10 years of civil war has proven is that the United States, lacking the capacity to put an end to the bloodshed, has "vital interests" in staying out of Lebanon, at least as long as other parties do too.

The Soviet Union, accustomed to exploiting political disorder anywhere, has in Lebanon shunned the kind of power vacuum into which it might normally move. Lebanon is lucky, so to speak, that the Cold War has not aggravated its troubles.

The Israelis in 1982 had the effrontery to think their army could establish a new order in Lebanon, only to withdraw in disarray, having lost 650 dead. More respectful of the Lebanese skill at killing, the Syrians have been more careful, using their own forces in Lebanon sparingly, chiefly to seal their border from a Lebanese contagion. For now, Israelis and Syrians seem willing to let Lebanon go its own way, a no-man's land, serving as a buffer between them.

So the civil war goes into its eleventh year, and no one seems to care, not even the Lebanese. What happened to the veneer of a once illustrious civilization? Is it possible that another society, even our own, could fall into such a barbarous pit? One day the Lebanese may wake up and decide they have had enough. But that day seems distant.