Yasser Arafat, frequently accused of only nominal control over often undisciplined Palestininan commando ranks, moved openly last week to assert his authority by arresting more than 100 alleged dissidents.

Arafat's new assertiveness has touched off a wave of indignation in commando ranks. One dissident guerrilla was killed an two others wounded in fighting with loyalist troops sent to arrest them in southern Lebanon.

Arafat however, was considered virtually certain by analysts to emerge with more authority from the showdown inside Fatha, the core group of the Palestine Liberation Organization he commands.

Despite various versions claiming the showndown stemmed from personal rivalries inside Fatah, the most popular view is that that the dissidents insisted on defying Arafat's authority by pressing plans to carry out behind-the-lines guerrilla attacks against the Israelis in southern Lebanon.

The fight broke out only hours after Arafat assured U.N. Secretary General Kurt Waldheim that the guerrillas would cooperate with the U.N. peacekeeping troops. The pledge indicated Palestinian willingness to refrain from attacking the withdrawing Israelis.

Analysts suggested Arafat may use his advantage to purge rivals inside Fatah for the first time in recent PLO history.

Lined up against him were such major Fatah figures as Aub Saleh, pro-Soviet leader traditionally favorable to extremist thinking, and Abu Daoud. Abu Daoud is a controversial commander who allegedly master-minded the 1972 killing of Israeli atheletes in the Munich Olympics.

Abu Daoud was reliably reported to be under virtual arrest in a Beirut hospital with armed guards outside his room.

Arafat supporters said he ordered the arrest because Abu Daoud had set up his training and operations command outside Fatah central control. Abu Daoud denied this.