JERUSALEM, SEPT. 13 -- The man who is widely considered to be a top leader of the Palestinian nationalist movement in the Israeli-occupied territories has been detained without charge for the third time in six months, an action denounced by Israeli and Palestinian human rights activists.

Faisel Husseini, a noted activist who is chairman of the Arab Studies Society, a legal, nonprofit cultural and political organization, was arrested late last night by agents of the Shin Bet, Israel's internal security service, who surrounded his house in Arab East Jerusalem, according to a spokesman for the society. Husseini, 47, is scion of one of Jerusalem's oldest and politically most influential clans.

Israeli authorities have called Husseini the chief operative and spokesman in the West Bank for Fatah, the dominant wing of the Palestine Liberation Organization, which is outlawed here as a terrorist organization seeking the overthrow of the Jewish state. Husseini has long denied engaging in illegal activities and to many Palestinians he has become a leading symbol of their effort to overcome the bonds of the 20-year-old occupation.

Israeli officials confirmed that Husseini was being held under a six-month detention order signed by Defense Minister Yitzhak Rabin but refused further comment. But Israeli radio cited a "security source" who said Husseini had been arrested because he had resumed his "illegal activities" after being released in July.

Husseini's supporters contend that he has been singled out for legal harassment because he heads a small, quasi-Marxist group called the Committee Confronting the Iron Fist. The group comprises Palestinians and Israelis who engage in demonstrations, hold press conferences and provide a steady stream of information to journalists on alleged "atrocities of the occupation."

A half-dozen Palestinian activists on the West Bank and Gaza Strip have been arrested and deported in recent months by the Israeli government. Israel says it is following defense regulations that were first used by Britain during its colonial rule and later by Jordan.

Although they were entitled to judicial review, those deported were expelled under administrative orders that did not entitle them to be informed of the specific charges against them or to face their accusers in court.

But because Husseini is a resident of East Jerusalem, annexed by Israel in 1967, Israel considers him subject to its civilian law. Many legal scholars contend that he cannot be deported unless convicted of criminal charges, even though Husseini technically remains a citizen of Jordan, which administered East Jerusalem before Israel captured it in the 1967 war.

Israeli security officials have contended that such charges cannot be brought to court without compromising intelligence sources. As a result, they say they have been forced to rely on administrative penalties such as detention without trial to constrain Husseini. But civil rights activists say such procedures are an abuse of Israel's legal system.

"We are extremely concerned," said Ruth Gavison, a Hebrew University law professor and leader of the Civil Rights Association of Israel, of Husseini's latest detention. "If the authorities have any solid evidence that he has broken the law, then they should arrest and charge him. If they can't come up with anything, then they have to let him go. Otherwise it seems to be a very clear case of harassment."

Husseini was subjected to five years of "town arrest," a modified form of house arrest, from 1982 until last April. He was detained without charge that same month during a security crackdown following violent protests and riots by school-age youths throughout the occupied territories over prison conditions for jailed Palestinians. The authorities at that time contended that Husseini was the main coordinator and strategist behind the widespread protests and commercial boycotts.

A High Court judge shortened his six-month detention order to three months. Husseini was released on July 9, but put under a new set of town arrest restrictions the next day. Under those orders, he could not leave Jerusalem's city limits, had to remain inside his house from dusk to dawn and had to report twice a week to the police.

On Aug. 26 he was picked up again for questioning, and held 10 days under a court order. He was released nine days ago.

"We are absolutely shocked," said Rada Shamali, a spokesman for the studies center. "He did nothing to provoke them to arrest him again. They claim he is politically active, but he is working in organizations that are legal and fully licensed."

She said two well-known civil rights lawyers, an Israeli Jew and a Palestinian, would seek Husseini's release in a court hearing Monday morning.

Husseini's clan has long claimed a leading role in the Palestinian movement. His father, Abdel Kader Husseini, was a commando leader during the struggle between Arabs and Jews for control of colonial Palestine and was killed just west of here in April 1948, a few weeks before Israel's independence. Another ancestor, Haj Amin Husseini, was mufti of Jerusalem for 30 years and a strident opponent of Zionism who sought unsuccessfully to forge an alliance with Hitler. The PLO's Yasser Arafat is also said to be distantly related to the clan.