SOME 900 years ago this week Pope Urban II issued a call from the French town of Clermont for European Christians to mobilize in a crusade to stamp out Islam.
The Crusades ended nearly 200 years later, but the spirit of mutual enmity they aroused has marched on unrelentingly through the centuries.
Now an international gathering of scholars and clerics is appealing for an end to the ever-smoldering sectarian strife. It has just issued a symbolic ''Declaration of Peace'' in this largely Protestant Swiss city on the German-French language frontier where a new Muslim mosque has been dedicated.
The four-page document - formulated by the Swiss Academy for Development (SAD) - proposes that:
* Christians, Muslims, and others try to understand each other the way they understand themselves.
* All faiths and religious skeptics support initiatives to develop school texts acceptable to all parties in history, geography, and other fields - particularly material about Islam and Christianity.
* Followers of both religions avoid abusing free speech when speaking and writing about the other religion.
* Wherever Christians, Muslims, and others live together a permanent interfaith council be set up to prevent violence and advocate human rights for all.
* Christians, Muslims, and others inside and outside Bosnia-Herzegovina work together to reconstruct the country.
* The mass media be urged to enter into a dialogue on ways in which it can promote peace through more responsible journalism.
Acting SAD chairman John Gaitung, a Norwegian social scientist and peace researcher, told the dialogue conference that Pope Urban II had acted nine centuries ago very much as religious extremists act today.
''He needed a common enemy,'' Professor Gaitung said, recalling the pope's effort to reunite Eastern and Western Christendom. ''He did exactly what would be done today. He had reports of extremist and fundamentalist Muslim acts and described them as 'typical.' His religious views allowed him to distort other religions in order to overcome them.''
Reacting to mention of ''Islamic fundamentalism'' in the same pejorative breath as ''extremism,'' Islamic speakers urged that it be avoided. ''It hurts,'' explained a member of Iran's parliament and his country's former United Nations ambassador, Said Rajai Khorasani. ''The concept of fundamentalism is not Islamic but Christian. We try to understand its meaning, but only through listening to you [Western Christians].''
A Greek Orthodox spokesman, Metropolitan Damaskinos of Geneva, agreed that ''Islam doesn't know the term,'' but added that ''both Christianity and Islam are characterized by the spirit of fundamentalism.'' He called this ''an attitude that one's faith and its experience are exclusively identical with truth,'' and said that it denied acceptance of others' faiths.
The Greek cleric said that he has engaged in an ecumenical dialogue with Crown Prince Hassan of Jordan since 1985. The two men have met five times in an effort to understand each other's religious views and to break down prejudices.
''Some 200,000 Muslims live in Switzerland today,'' pointed out Farhad Afshar, an Iranian development sociologist at the University of Bern. ''But we are not permitted to have a cemetery [of our own].''
Muslim speakers, including Iranian Ayatollah Mohamed Taghi Jafari, also deplored the role of the media for fanning the flames of Islamic-Christian disputes. ''We need to invest in eliminating ignorance,'' the ayatollah told the forum. ''Future epochs will look back upon our [warring] behavior today as we look upon the era of slavery.''