Though the hijacking of a Kuwaiti jumbo jet hasn't set any records yet, it has still become one of the longest such episodes on record.

As this deadly war of nerves has worn on, it should have taught some new lessons as well as reinforced old ones for hijackers and for those seeking to combat this form of terrorism.One of those lessons is that such hijackers could be getting more sophisticated. The latest hijacking, now in its ninth day, was certainly well-planned. Some of those who commandeered the jumbo jet on a flight from Thailand to Kuwait seem familiar with airplane and airport operations. One of them is said to have described himself as a former flight engineer. Technically sophisticated fanatics can, of course, be especially dangerous.

Another lesson is that safe havens for hijackers could, to some extent, be drying up. The pirated Kuwaiti plane was turned away from both Lebanon and Iran before flying on to Cyprus, then to Algeria. This cold-shoulder treatment seems particularly significant because the hijackers, who appear to be Shiite Moslems, evidently have ties with both Lebanon and Iran.

Could it be that those who normally sympathize with the objectives of Middle East terrorists are starting to learn that depredations against helpless airline passengers accomplish little except to discredit the very cause the hijackers seek to further?

Still another lesson is that security for air travelers can be no stronger than the weakest link among the various international airports. In the case at hand, hijackers of the Kuwaiti plane may have smuggled aboard their weapons in Bangkok through a ramp area used by caterers and cleaning crews. Wherever it happened, that weak link must be pinpointed and strengthened.

Then there's the way this hijacking has focused international attention on the Palestine Liberation Organization. It's the PLO that has conducted the most extensive negotiations so far aimed at freeing the passengers of the Kuwaiti jet. Success in bringing a peaceful end to the hijacking could boost the PLO at a time when it is trying hard to win a role in the Middle East peace initiative being conducted by Secretary of State George Shultz.

The hijacking also has drawn world attention to the grit and fortitude of Kuwait, a small country constantly needing to balance off big neighbors Iran, Iraq, and Saudi Arabia and diverse segments of its own population.

After pro-Iranian Shiites launched a wave of bombings in 1983, the Kuwaitis handed down death and prison sentences for the perpetrators, knowing that the tough punishment would bring on a succession of terrorist reprisals like the present effort by the plane hijackers to free some of their comrades. Despite the torture and killing of at least two passengers, the government of Kuwait has refused so far to knuckle under to this murderous blackmail.

Whatever the final upshot of this particular ordeal may be, it's bottom line is still the same as all other terrorist hijackings: the most effective way to deter blackmailers of any kind is to refuse to pay their price, costly as such refusals may sometimes be.