A controversy has arisen over the scheduled dates for next year's joint annual meeting of the World Bank and International Monetary Fund in Toronto because they conflict with the Muslim festival of Idd Ul-Adha.

This holiday, one of the two most important in the Islamic religion, is a feast marking the end of the annual pilgrimage to Mecca. It is said to be "even more important" than the holy month of Ramadan." One official said it is of the same relative order of importance as Christmas is for Christians.

A group of Arab nations formally petitioned the IMF and bank at last week's sessions here to change the dates for the Toronto meeting -- Sept. 28 through Oct. 1, l982 -- to avoid the conflict. The matter was referred last Friday to the executive directors of both agencies "on an urgent basis" by the Joint Procedures Committee.

But Canadian officials, to whom the Arab group have appealed separately, have said that it will be difficult to get hotel space for the meetings at any other time. This year, 10,500 officials and guests were registered for the annual meetings just concluded in Washington.

In 1975, at the request of the Arab nations, the annual meeting was advanced to the end of August from the end of September to avoid a conflict with Ramadan. Officials said yesterday that so far as they know, no conflicts with Ramadan are likely for many years to come.

At the annual meeting which ended last week in Washington, the first two days of the four-day session coincided with Rosh Hashanah, the Jewish new year. Israeli officials last summer had expressed their regret over the schedule for the 1981 meeting, but World Bank-IMF officials, who said they had received no other complaints, told the Israelis they had not been aware of the potential conflict, and there was not enough time in any event to shift the dates. The Israeli central bank has sent bank-IMF officials a 10-year calendar showing the dates of Rosh Hashanah and the other Jewish high holy days.

Conflicts with Jewish high holy days have been frequent in recent years. The Jewish new year also coincided with the annual meetings in 1973 in Nairobi and in 1979 in Belgrade, and Yom Kippur, the Jewish day of atonement, coincided with the annual meeting in 1976 in Manila.

Some non-Israeli government officials, some employes of the bank who are Jewish, and members of the Israeli delegation did not attend last week's opening session, which addressed by President Reagan. Following Orthodox Jewish custom of two days observance for such holy days, the Israelis also did not attend the second day's official sessions or private caucuses because "that would have given us political problems at home," an Israeli central bank official explained.

Now Saudi Arabia and other nations are threatening to boycott the sessions in Toronto unless they are shifted to avoid the conflict with Idd ul-Adha. If the dates of the Toronto session cannot be shifted because of hotel commitments, it could have an ironic effect on the potential admission of the Palestine Liberation Organization as observers, a status they have been seeking since 1979 with the support of the Arab bloc.

It had been expected that the PLO -- which was rebuffed last week for the third successive year in its effort to get seated at the sessions -- finally might make it at Toronto because a Kuwaiti is scheduled to be the chairman of the session. The chairman has the power to bring the question to a floor vote.

But if the Kuwaitis and other Islamic nations should boycott the sessions leaving the chair to someone else, that opportunity might be lost to the PLO.