One can only share in the joy of the Robert Polhill family, which has been reunited with their father, a professor of business and accounting at Beirut University who was captured, shackled and jailed for 3 1/2 years, a prisoner of Islamic extremists who once had planned to barter his freedom for arms and political concessions.

The relief at Polhill’s release from the custody of pro-Iranian Shiite Moslems is tempered by the knowledge that there are seven more Americans and 10 other Westerners who remain in captivity in Lebanon.

As Polhill himself observed, almost in a single breath: He is genuinely happy to have his freedom, but remains deeply concerned about the fate of two fellow educators, Alann Steen and Jesse Turner, both of whom were swept with him into captivity in January 1987. Polhill is free. By this time next week, these men will have spent 1,190 days in confinement.

For appearances, the United States officially has thanked the governments of Syria and Iran for their assistance in gaining the release of the hostages. There is the prospect that other hostages may be released unconditionally later this week, and therefore the pretense of gratitude will continue to these two nations, which continue to be a major part of the problem in the Middle East.

The hostages indeed may come home, but not because of any humanitarian concerns in Tehran or Damascus. If they are released it is because they have ceased to be an asset to their jailers. Terrorism now is recognized as a dangerous, unproductive foreign policy, even for relatively impotent political factions. With the death of Khomeini and more important, the rapid dissolution of the Soviet empire, the Shiites, Syrians and Iranians all have been sawed off — left holding the keys, but with nothing to gain by keeping innocent people in captivity.

Under the circumstances, with 17 Westerners still in captivity, America’s political leaders may have to issue an obligatory “thank you” to Syria and Iran, but the people of this country know that these nations could have prevented this miserable, barbaric and now failed policy from being instituted in the first place.