LT. COL. William Higgins, a Marine officer on a peace-keeping mission, becomes the ninth American hostage in Lebanon. He was seized by one of the arms or offshoots or competitors of Hezbollah, agents that revolutionary Iran dispatched to Lebanon in the chaos born of the Israeli invasion of 1982. Most Israeli soldiers eventually went home, but the fundamentalist terrorist Party of God stayed on.

The colonel was among a small number of Americans serving in the 17-nation United Nations Truce Supervision Organization (UNTSO), which was set up in 1949 to supervise the Arab-Israeli truce on all of Israel's borders. Later, after the 1978 Israeli invasion, the separate U.N. Interim Force in Lebanon (UNIFIL) was set up; it has no Americans. The smaller and less conspicuous UNTSO has long stood apart from the general turmoil. The U.N. flag provided a measure of protection, and UNTSO's mission did not put it where UNIFIL stands -- smack in the middle of feuding Lebanese. Perhaps a local fix was in. But now something has changed.

As usual, rescue is difficult and reprisal is dangerous. Presumably, the American government, for all its rage and frustration, is not going to go down the Iran road again and offer a consideration for the colonel and for the eight other American hostages. The first responsibility for securing their return remains with Syria, would-be controlling power in Lebanon, and especially with its surrogate in south Lebanon, the moderate Shiite militia of Amal. In the next circle lies what possibility there may be to wrap return of hostages into U.N.-sponsored negotiations to end the Gulf war.

With UNTSO's inviolability broken, should American colleagues of Col. Higgins in the group remain in Lebanon? Obviously, the security procedures have to be thoroughly reviewed. It's evident, though, that a withdrawal would be at very heavy cost: the United States has never stopped urging other nations to live with the risks to which their nationals are exposed in U.N. peace-keeping missions in Lebanon and elsewhere. This sort of pressure on either one of the U.N. presences in Lebanon could only make the appalling situation there worse.

Whatever happens, humane people everywhere will know that the hostage-takers and their patrons are brutal people requiring a calculated response but deserving of total contempt.