Jason Robards played Soviet dissident Andrei Sakharov in a Home Box Office movie but never met him.

Yesterday, however, the actor did meet the only accessible relative of the nuclear physicist who has been called the "the father of the Soviet H-bomb."

Robards made the acquaintance of Sakharov's stepson, Alexsey Semyonov, 29, outside the Soviet embassy, where he was in the eighth day of a hunger strike to protest his parents' exile in Gorki, some 250 miles from Moscow.

"If they would give me a visa, I would go and meet him. I've got nothing against Russia," Robards said.

Robards arrived at the corner of 16th and K streets NW in the blistering heat at about 4 p.m. He shook hands with Semyonov and his sister, Tanya Yankelevich, who arrived from Boston Thursday to join him.

One or two curious passers-by gathered at the spot on recognizing the actor who is now appearing in "The Iceman Cometh" at the Kennedy Center. Robards said: "There is no explanation for this silence. I'll try to see anybody, meet anybody . . . it's the only thing I can do. It's kinda striking in the dark because I don't know any background," he said.

Robards said he would publicly appeal to President Reagan, if it would do any good. "I'll have to find a way to approach him Reagan . I don't know him." He then signed a petition urging Reagan and Secretary of State George Shultz to intervene and free Sakharov and his wife, Yelena Bonner, adding his name to about 150 others.

According to Semyonov, the petition was prepared by a secretary, Gloria F. Priest, who works in one of the office buildings nearby. He said she came to him Thursday and said she wanted to do her bit to help. She then typed several copies of the petition and hung it by the table next to Semyonov.

Semyonov said that according to reports from Germany, his parents are not in their apartment in Gorki. "I am not even sure if they are alive." He also said he has had only mineral water in a week.