Marxist historian Roy Medvedev and a woman who tried to flee the Soviet Union last year in a Piper Cub today were named as candidates by a Moscow voters' group to challenge the official Communist Party nominees for the Supreme Soviet in elections next month.

The group, calling itself "Election '79," told Western reporters at a press conference that they chose Medvedev, a former Communist Party member whose historical works on Stalin and other contemporary themes of Soviet life are widely circulated in the West, after dissident figure Andrei Sakharov refused to accept their support.

Medvedev, who was not present at the press conference, later told reporters he believed the move was a "political experiment," not a form of dissent.

No one can recall such an independent move in the Soviet Union, where Communist Party candidates for the Supreme Soviet, or parliament, are carefully chosen and certified well before the election. They are normally the only nominees for the job.

About two dozen persons identified themselves as supporters of Medvedev for the Supreme Soviet of the Republics, one of two houses in the bicameral parliament. The official candidate is Bolshoi Theater prima ballerina Natalya Bessmertnova.

Medvedev, 53, was reported to have said that if his nomination is accepted, he will seek election in the March 4 nationwide poll. He is being proposed as a candidate from Sverdlovski city election district.

The loose-knit voters group also said it will seek official certification for Lyudmilla Agapova, 40, who has sought without success to emigrate from the Soviet Union to join her husband, a seaman who jumped ship some years ago in Sweden and became a political defector. Last spring, Agapova said she had tried to be flown out of the Soviet Union in a light plane that landed on a frozen lake north of Leningrad. But the aircraft landed and took off before she could reach the rendezvous point, she said.

Her story never has been corrobrated by the tight-lipped Soviets, but Finnish authorities detained the pilot of a light plane in the border area near where she said the rendezvous point was.

The leader of the election group, photographer Vladimir Sychoc, said he will learn Saturday whether authorities at the local election board office will certify the two as legal candidates. He said Agapova will run as a candidate from a region outside Moscow for the Soviet of Nationalities, the other parliamentary house.

Sychov said competition for the posts would "further perfect" socialism in the Soviet Union. Traditionally, only one candidate is offered for any elected office here. While fewer than half the members of the two houses are Communist Party members, their candidacies are approved by local party committees.