BEIRUT, AUG. 21 -- The Iranian-sponsored Islamic Jihad organization announced tonight that one of its three French captives is "gravely ill," accused Kuwait of torturing 17 Shiite Moslem prisoners and threatened to retaliate against its own hostages.

The group delivered a typewritten statement in Arabic accompanied by videotaped messages from two of the French hostages, journalist Jean-Paul Kauffmann and diplomat Marcel Carton, to the offices of an international news agency in west Beirut.

"One of the French hostages is gravely ill and we assert that if they are in danger then the responsibility lies entirely with the Great Satan America and its tool France," Islamic Jihad said. Islamic Jihad claims to be holding Kauffmann, Carton, diplomat Marcel Fontaine and two Americans -- journalist Terry Anderson and agronomist Thomas Sutherland.

{News agencies reported that Ash-Shiraa, the Beirut weekly magazine that last year disclosed U.S. arms shipments to Iran, said in its Saturday edition that missing Anglican Church envoy Terry Waite and two West German hostages would be freed "very soon" in a $5 million deal worked out by a Lebanese leader and their Moslem extremist captors.}

The pro-Iranian Islamic Jihad, which seized its French and American captives between March and May 1985, repeatedly has demanded the release of 17 Shiite prisoners convicted in Kuwait of bombing French, American and Kuwaiti targets in December 1983.

Islamic Jihad gave Kuwait a 15-day ultimatum to issue filmed interviews with the prisoners before it starts "mistreating the hostages" and threatened to withhold "any future news on them."

The group warned that it would start maltreating its own captives if Kuwait did not end the "severe psychological and physical torture" of its Shiite prisoners. Neither of the French hostages appearing on the tape mentioned which hostage is ill or what the illness is.