Two prominent West Bank Arab mayors, expelled by Israel last May and allowed to return this week to appeal their case, were imprisoned today until a military tribunal rules on their plea.

Israeli military authorities turned down a request by Fahd Kawasme, mayor of Hebron, and Mohammed Milhem, mayor of Halhoul, to be allowed to spend Aid al-Adha, a festive Moslem holiday, with their families.

The two have been in detention since their arrest Tuesday, when they crossed from Jordan to the Israeli-occupied West Bank, and a special military tribunal has been questioning them in closed hearings in a makeshift courtroom in a border customs facility.

Although the two have vehemently denied the government's charge that they incited violent resistance against the Israeli occupation, according to Israeli press accounts, they are pessimistic and fear that the expulsion order will be upheld.

Haaretz, a leading Israeli daily newspaper, reported that Israeli security officials testifying before the tribunal presented a detailed case against the two mayors, including tape recordings and film strips, to support the government's assertion that the return of the mayors could cause renewed unrest in the occupied territories, which have been relatively quiet in recent weeks.

Kawasme and Milhem were forcibly expelled to Lebanon during the night on May 3, just hours after six Israeli settlers were killed in an attack in Hebron.

They have traveled to Europe, the United States and United Nations since then in an effort to draw attention to their case and the situation in the Israeli-occupied territories. Two weeks ago Israeli Prime Minister Menachem Begin agreed to allow them to return to Israel to petition for withdrawal of the expulsion order. The military tribunal is expected to rule on Sunday or Monday and, sources here predict, the mayors will be allowed to appeal to Israel's supreme court if the ruling goes against them.

When Milhem and Kawasme crossed the Allenby Bridge, which connects Jordan and the West Bank, on Tuesday they were arrested and held temporarily in detention facilities at the border, until their imprisonment today.