Three released hostages from the TWA hijacking, including Greek singer Demis Roussos, today provided new details on the separate removal of passengers with Jewish-sounding names from the rest of the hostages on Saturday.

They suggested that until yesterday morning, at least four members of this separate group were being decently treated.

Roussos, his American secretary, Pamela Smith, and Arthur Targondtsidis, an 18-year-old student from Brockton, Mass., spoke at dockside after arriving by overnight boat from Lebanon. As local reporters pressed in on Roussos, a major celebrity in the region, many journalists were unable to hear what was being said.

But U.S. Embassy aide Dan Howard, who met with the three former hostages before they boarded a flight to Athens, gave some details of their conversation:

Targondtsidis said he was taken off the Boeing 727 when it landed for the second time in Beirut and one passenger was executed. With Targondtsidis were four other men. He said his captors believed the other four to be Jews because of the names on their passports. The names of those believed to be in that group have not been made public. But interviews with other hostages released in Algiers suggest that one name is Schwartz, another is Trautmann.

Roussos and Smith were removed from the plane at about the same time, but apparently in a different group. Roussos was vague today about the exact number but said there were four or five people taken off the plane with him as well.

Targondtsidis said that he had not seen Roussos or Smith until he met them at the press conference with Nabih Berri on Tuesday morning announcing their release.

If so, then as many as 10 or 11 people may have been removed from the plane Saturday, and three of them have now been released.