The domestic soccer league has yet to begin but this week two of the country’s leading clubs, last year’s champion Panathinaikos and runner-up Olympiakos, begin their quests in the Champions League, Europe’s most prestigious club-level competition. Panathinaikos opens the country’s Champions League proceedings for the season tomorrow night at home against Rosenborg, a bitter memory in the past for the Greek team. The Norwegian club deprived Panathinaikos of a berth in August 1996 in the preliminary qualifiers. It was a great letdown for the Greek club which had enjoyed a fabulous run to the Champions League semifinals in the previous season. Panathinaikos, which drew a place in Group E, will also face Arsenal and PSV Eindhoven. To do well, the Greek team will need to improve on a troubling Greek Cup performance just days ago, a hard-fought 3-2 home win over third-division club Atsalenios in the competition’s first round. A second leg remains. On Wednesday, Olympiakos travels to Spain to meet Deportivo in a Group A match. Liverpool and Monaco, last year’s runner-up, have also drawn into the group. The two top-placed sides from eight groups advance to the competition’s knockout phase.