The Soviet Union's supersonic airliner, the Tupolev-144, has been quietly withdrawn from passenger service for unexplained reasons, it was learned yesterday.

The move was disclosed by an Aeroflot employe, who told a would-be passenger by telephone that the plane, rival of the Anglo-French Concorde, would not be flying this year.

Callers who made further inquiries to Aeroflot, the Soviet state airline, were told it was not known when the plane would be back in service.

The trouble-plagued TU-144 made its maiden passenger flight 10 months ago to the central Asian city of Alma-Ata. It was scheduled to continue flying there and back each Tuesday from Moscow's Domodedovo Airport.

Western diplomatic sources said they understood the service was curtailed in early June, although two of the planes were seen parked at Domodedovo last week.

The sources said a possible reason was the plane's reportedly poor fuel economy. This might also be why Aeroflot had so far not used the TU-144 on longer routes thatn the 2000 miles between Moscow and ALma-Ata.

Western speculation about a fuel problem began hell before the Tupolev's first passenger flight in 1968 and its first passen-commercial interest in British-made equipment to control air and fuel flow into jet engines.

The TU-144 made its first test flight in 1968 and its passenger flight has initially scheduled for 1973 - the year one of the planes crashed at the Paris Air Show, killing the crew and eight people on the ground.

Despite the ensuing four-year delay, the Soviet Union made the most of the occasion when passengers first boarded the airliner last Nov. 1. They were served cognac and caviar, and told by a hostess that the flight was the Soviet Union't biggest scientific and technical achievement in recent years.