Portuguese police said today that they believe a commando-style group was involved in Sunday's assassination of leading Palestine Liberation Organization moderate Issam Sartawi.

In a statement late today, police said examination of eyewitnesses' accounts pointed to the involvement of several people in the shooting of Sartawi, the PLO's 47-year-old European representative, at the hotel in southern Portugal where he was attending a congress of the Socialist International. One man is being held.

Two people present, including Sartawi's secretary, Anwar Abu Eisheh, who was hit in the thigh, said they thought they saw two gunmen, but the majority of eyewitnesses said there was only one assailant.

Acting Interior Minister Roberto Carneiro identified the detained man as 26-year-old Youssef Awad, arrested holding a Moroccan passport police believe may have been forged. Carneiro said the man was seized at a Lisbon hotel 11 hours after the Sunday morning attack in Albufeira. He said Awad had entered Portugal from Spain last Friday.

Sartawi, a moderate within the PLO who advocated dialogue between Palestinians and Israelis, was killed with five bullets to the head and chest. A hard-line Palestinian group led by Abu Nidal claimed responsibility for the killing.