Hoping for a cease-fire to commemorate Aid al-Adha, one of the most joyous feasts in the Moslem calendar, Secretary General Habib Chatti of the Islamic Conference arrived here today to renew his efforts to end the 25-day-old war between Iraq and Iran.

Chatti accompanied President Mohammed Zia ul-Haq of Pakistan on a fruitless mediation effort to Baghdad and Tehran just after the war broke out. This time alone, he was to meet with President Saddam Hussein and other high Iraqi officials before reporting back to Zia, chairman of the 40-nation Islamic group. He will then proceed to Tehran for a second round of talks with representatives of Ayatollah Ruhollah Khomeini's Islamic Republic.

According to Middle East diplomats here, Chatti is hoping that the advent of the four-day feast will provide the impetus for the two Moslem nations to stop fighting, if only for the duration of the holiday. Depending on the rise of the moon, Aid al-Adha will begin Sunday or Monday with the ritual public slaughter of sheep.

Chatti is given no chance of mediating a final end to the war now where he failed earlier. But a temporary cease-fire is not totally ruled out yet.

The mullahs who run Iran have been adamant since the war began that they will not accept a cease-fire so long as Iraqi troops are on Iranian soil. With a huge Iraqi Army occupying large tracts of Iran's Khuzestan Province and besieging its cities of Khorramshahr, Abadan and Ahwaz, no one here believes that the mullahs will change their mind now.

Chatti, however, is trying to convince both sides that even if they cannot agree to terms for a permanent cease-fire, they should stop fighting during the Aid, a time of exuberant feasting around the Islamic world. Not only would that perhaps open the door for further talks, but it would also allow for the estimated 100 foreign ships trapped in the disputed Shatt-al-Arab waterway that divides the two countries to slip out to safety in the Persian Gulf before the hostilities resume.

Hussein, who two weeks ago proposed his own four-day cease-fire only to have it refused by the Iranians, is expected to agree to Chatti's proposal, according to Arab ambassadors here. Hussein is believed to sincerely want a cease-fire before the war he began for limited goals gets out of hand.

"Saddam Hussein has nothing to lose by a cease-fire in place," said one Arab ambassador here. "In fact he has everything to gain by accepting Chatti's proposal."

With his army clearly holding the initiative inside Iran, a cease-fire would not only hold his strategic advantage but also become an uplifting boost for the morale of the troops in the field. Hussein's acceptance of a cease-fire would also go some way toward restoring some of the prestige he lost in the Third World for having started the war against his OPEC neighbor in the first place.

Since Iraq's initial objectives in the war were limited to settling contested borders and establishing its sovereignty over the Shatti-al-Arab, a cease-fire now would help consolidate those goals, which a widening war and its unpredictable consequences could still threaten.

Chatti, Arab sources here maintain, decided the time was ripe to resume his mediation efforts after Iran's President Abol Hassan Bani-Sadr last week indicated willingness to agree to a limited United Nations cease-fire to allow foreign freighters to leave the Shatt-al-Arab.

But senior Western and Arab diplomats in Baghdad are not overly optimistic that Bani-Sadr's statement will indeed lead to even a temporary cease-fire. They point out that the U.S. hostage crisis in Iran has amply proved in the past that there is a wide gulf between what Bani-Sadr promises and what he can produce. Some diplomats even insist that Bani-Sadr may relish a continuation of the war, if only because it has strengthened his hand against the mullahs who consistently oppose him.

Senior diplomats here fear that the same vacuum of power that has frustrated every effort to negotiate the freedom of U.S. hostages in Tehran, will now frustrate every effort by Saddam Hussein, or intermediaries like Chatti, to negotiate a cease-fire that would lead to an end to the war.

"Saddam Hussein has failed to learn from the U.S. experience in Iran," said one Middle Eastern ambassador. "He hoped for a quick war in which his advantages in the field could then be translated into political concessions at the negotiating table. What he failed to perceive was that in Iran there are still no interlocutors with whom to negotiate."