Israeli troops sealed off the roads to Gaza City today in an attempt to block a one-day hunger strike by Arab mayors in support of the mayor of Nablus, who was arrested and ordered departed for allegedly expressing sympathies for the Palestine Liberation Organization.

The Israelis acted while Palestinians in the West Bank and Gaza Strip demonstrated with hunger strikes, business shutdowns and sit-ins to show their backing for the mayor, Bassam Shaka.

Soldiers stopped some of the mayors as they left their West Bank towns. They stopped others at the edge of Gaza. Gaza Mayor Rashid Shawa was turned back before he had walked 100 yards from his home.

Bethlehem Mayor Elias Freiji, who was held at a roadblock on the outskirts of Gaza, said he regarded the Israeli move as a contravention of an earlier promise to West Bank leaders of freedom of movement and speech..

The Palestinians' protests were nonviolent except for one reported rockthrowing incident in the Arab sector of Jerusalem.

Shaka was arrested last Sunday, and the Israeli government formally decided on Wednesday to banish him from the occupied West Bank of the Jordan River, where he is mayor of the largest town, Nablus.

The government claims Shaka is sympathetic to Plo terrorist attacks and cites his record of resistance to Iraeli rule and frequent anti-Israeli statements, which it says amount to incitement. Shaka has appealed the deportation order to Israeli's High Court, which has scheduled a hearing on the case for Thursday.

Today's hunger strikes were declared in sympathy with Shaka, who refused solid-food for the second day.

All three West Bank universities were closed today, normally a school day, and a group of Arab students at Najr University in Nablus announced a one-day hunger strike.

Seven mayors from the Ramallah area were blocked on the road to Gaza. They went to the neighboring town of El Bireh, took over the Red Cross office there and fasted for the day.

"We will continue to fast until tomorrow morning," Ramallah Mayor Kerim Khalaf said in a telphone interview.

Meantime, Israeli Maj. Gen. Danny Matt, a key figure in the Shaka controversy, was reported to have been removed from his post as the official in charge of political administration in the occupied area. Shaka's statments allegedly sympathetic to the PLO were made in a private conversation he had with Matt.