BEIRUT, Lebanon--Lebanon's top Shiite Muslim cleric said yesterday that a Western hostage would be released in weeks, but urged a one-time swap involving the captives and Arab prisoners to end the crisis.

Sheik Mohammed Mehdi Shamseddine's statements came amid intense speculation that freedom for one or two of the Western hostages was imminent. Other religious leaders with ties to the kidnappers had predicted a hostage release in a matter of days.

Shamseddine called for a comprehensive swap--rather than gradual releases--of Arab prisoners held by Israel in return for the 11 Westerners held by Shiites in Lebanon. But Israel says the detainees will only be freed after a full accounting of its seven missing servicemen.

Amid other signs of movement on the hostage issue, Iran's foreign minister, Ali Akbar Velayati, called for all parties to cooperate with U.N. Secretary-General Javier Perez de Cuellar, who is leading diplomatic efforts to free the captives.

Iran has helped secure the release of hostages in Lebanon in recent years, and backs the Shiite extremist group Hezbollah, or Party of God, that reportedly controls factions holding the hostages.

Officials in Syria, the main power broker in Lebanon and the first stop for most released hostages, also said yesterday that they have been on constant alert since Wednesday.

When asked about a possible release, however, Shamseddine said:

"I can't say in a matter of days, but I can say in a matter of weeks--provided that American and Western pressure continues to be put on Israel to release further Arab prisoners from Israeli prisons," he told the British Broadcasting Corp.

Last week, Israel's proxy militia in Lebanon freed 51 of its 300 to 400 Arab prisoners and returned the remains of nine Lebanese guerillas after receiving evidence that one of the missing Israeli soldiers had died.

But the cleric advised that releases should be made all at once.

"We have strongly recommended that the deal for the release of all hostages should be comprehensive and complete and should not take place in stages, for fear some unexpected obstacles crop up," Shamseddine told the BBC.

The sheikh also said that he couldn't predict the nationality of the next hostage freed. Speculation has focused on Jack Mann, a 77-year-old former Royal Air Force pilot who has been missing for two years.

Shamseddine, who heads the Higher Shiite Council, said "the prospects for releasing Western hostages are good--but I cannot say whether the hostage to be released will be British or American."

His remarks came a day after two well-informed sources predicted a quick release of a captive.

Sheik Ahmed Taleb, a Shiite Muslim cleric with ties to the kidnappers, said Saturday from his home in Jibsheet, south Lebanon that a hostage, probably a Briton, would be released.

Also, the English-language Tehran Times newspaper, which is close to Iran's President Hashemi Rafsanjani and has accurately predicted hostage releases before, said a Western hostage could be freed soon.

From Tehran, Velayati didn't make any predictions, but he expressed support yesterday for the efforts of Perez de Cuellar, who ended three days of talks on the hostages with Iranian leaders on Friday.

Referring to four Iranians who disappeared in Lebanon in 1982, Velayati said: "We are the first victims of that problem and we hope that the efforts of the secretary-general will help in reaching a comprehensive solution to the problem."

Held in Lebanon are five Americans, three Britons, two west Germans and an Italian. The longest-held is Terry Anderson, 43, chief Middle East correspondent of The Associated Press. He was kidnapped in Beirut on March 16, 1985.