ATHENS, Greece (AP) _ The head of a Libyan-based, pro-Palestinian group on Friday told delegates to an international conference on terrorism that the United States was ''a barbaric aggressor and superpower terrorist.''

''Light should be shed on this terrorism that is practiced by states, especially the United States,'' Omar El Hamdi told more than 70 delegates from over 30 countries.

The three-day conference was organized by the Communist-backed Institute for the Study of the Greek Economy and partly sponsored by El Hamdi's International Secretariat for Solidarity with the Arab people and their Central Cause: Palestine.

Officials said the conference had no connection with Greece's socialist government. Greece has been criticized by its Western allies this year for not condemning nations by name for their alleged involvement in terrorism and not applying Common Market sanctions against Libya and Syria.

Institute president Marios Nikolinakos said the meeting was aimed at ''studying the philosophy, ideology and practice of terrorism as a new doctrine.''

''It seems that state terrorism will develop in the future as an ideological weapon ...,'' Nikolinakos said. He was the unsuccessful Communist candidate earlier this year for mayor Piraeus, the port city adjoining Athens.

Conference organizers said the delegates were ''university professors, researchers and representatives from labor unions and political organizations.''

The delegates included citizens of Syria, Libya, the Soviet Union, Cuba, Czechoslovakia, Hungary and Yugoslavia as well as Britain, the United States, Canada, France and Italy.