The days of wrangling drew in President Clinton as a major mediator, and Israel was eventually forced to release Sheik Ahmed Yassin, the founder and spiritual leader of the Hamas movement. Moreover, Mr. Netanyahu came under strong American pressure to release additional scores of Hamas prisoners because the King was threatening a total breach of relations, the closure of the Israeli Embassy and a public trial by military court of the two Israeli agents, according to participants in the negotiations.

''Did we get to the brink?'' said Crown Prince Hassan in an interview at the Royal Palace last Sunday. ''Yes, we got to the brink.''

The exact nature of the toxin used to attack Mr. Meshal, who now appears fully recovered, is a closely-guarded secret here and in Israel. But according to accounts by people closely involved in the subsequent arm-twisting, who insisted on anonymity, Israel eventually told Jordan that the assailants had used a high-tech and previously unknown delivery system to blast a fatal overdose of a synthetic opiate called Fentanyl through his skin.

The delivery system remains a mystery: Jordanian officials insist that no device was found, and diplomats were left to speculate that it was perhaps some form of miniaturized gas canister that the assailants abandoned in a getaway car whose driver sped off after the assailants jumped out. The drug is in wide use in anesthesiology, usually in small controlled doses to control pain. But it is said to be 50 to 100 times more powerful by weight than morphine and an overdose is usually fatal, according to doctors in Europe.

An Offer to Mediate And Then the Attack

According to those physicians, the drug can be given orally, by injection or through the skin in what is called transdermal delivery. The body metabolizes it quickly -- meaning that traces of it in Mr. Meshal would likely have dispersed rapidly.

Mr. Netanyahu is thought to have authorized the operation in reprisal for a Hamas suicide-bombing in Jerusalem on July 30 that killed 16 Israelis. His rationale was that, as an Israeli statement put it, Mr. Meshal was ''the pre-eminent figure in Hamas and responsible for the murder of innocent Israeli civilians.'' Yet, by many Jordanian and Western accounts, Mr. Meshal limits his activities to what a diplomat called low-level ''propaganda and rhetoric,'' and it is the Hamas military wing based in Damascus that is held responsible for planning suicide bombings.

The timing also seemed odd. Only two days before the attempt, Jordan transmitted to Israel what it described as an offer to mediate with Hamas for a moratorium on suicide bombings, according to diplomats and King Hussein himself in a speech last week.