Israel's highest court today rejected an appeal to overturn the deportation order last May of two leading West Bank mayors and an Islamic judge but at the same time sharply criticized the military government for "grave improprieties" which it said accompanied the explusion of the Palestinian leaders.

The Supreme Court recommended that if the two mayors -- Faad Kawasme of Hebron and Mohammed Milhem of Halhoul -- disavow past denunciations of Israel and pledge to obey West Bank military government law, they be allowed to return long enough to state there case to a military appeals advisory board.

However, the third deportee, Sheik Rajik Tamimi of Hebron, should not be allowed to return to make an appeal between he openly advocated the destruction of Israel, the court said.

Two of the trhee High Court justices severely reprimanded the military government for the manner in which hours after six Jewish settlers were slain in an Arab machine-gun ambush in hebron.

The three West Bank figures were issued explusion orders and told that they were being taken to meet then Defense Minister Ezer Weizman. Instead, they were blindfolded and taken by Army helicopter to the Lebanese border, where they were put across into Palestinian guerrilla-held territory without any opportunity to appeal.

The deportations, coupled with bombing attacks a month later on the mayors of Nabtus and Ramallah, stripped the West Bank of any effective leadership and effectively disbanded the Palestinian National Guidance Committee, the only nationalist organization in the West Bank. While no arrests have been made in the bombings, they are widely believed to have been carried out by ultranationalist, Jewish civilian settlers.

Kawasme and Milhelm, who were in Amman today awaiting the court decision, vowed to continue their struggle until they are allowed to return. They said they will increase-their efforts to rally international public opinion against the deportations and are planning a trip to Moscow next month. o

The vote against the mayors was 2 to 1, with Justice Chaim Cohen writing in a dissenting opinion that as soon as the deportation orders were written, the three West Bank figures were entitled to an appeal before the military advisory board. Since they were denied due process, Cohen said, the deportation orders are invalid and the appellants should be allowed to return.

The two mayors' attorney, Felicia Langer, said Cohen's dissenting opinion was a "positive step."

Both Cohen and Justice Moshe Landeau maintained an appeal could have been made quickly, with Landeau adding, "With all due respect to the task of those responsible for security, we must once again remind them that they are subject to the law, and that concern for the implementation of the law is not an obstacle but a duty which much be carried out under all circumstances."

Landeau said he was aware of the military government's opposition to readmitting the mayors under any conditions. But he said he wondered whether the authorities had taken into consideration the possibility of unrest in the West Bank "should the population become aware that an illegal act carried out by the authorities has been allowed to stand uncorrected." However, he said the deportation order should not be overturned.

Justice Yitzhak Kahame argued that an "emergency" and the "need for immediate protection of the public" outweighed all other considerations including the right of due process.