Soviet President Leonid Brezhnev was absent from yesterday's meeting of the Supreme Soviet, whose sessions he has always attended in the past, and the leader also has canceled a meeting scheduled for today with Willy Brandt.

Brezhnev also missed the opening meeting Wednesday of the Soviet Parliament's three-day winter session, causing speculation that he may be unwell.

Some diplomats noted that Brehnev, who will be 71 on Monday, was only recently confirmed as president of the Supreme Soviet and would have been expected to attend.

Brezhnev last appeared in public Dec.7 but was officially reported to have addressed a long speech to the Communist Party Central Committee Tuesday. His health has been a source of speculation since he dropped out of public sight for about six weeks in 1974, when some sources speculated that he had undergone jaw surgery.

Last spring and summer some French and Americn diplomats said he seemed to be in declining health but he returned from a Crimean vacation apparently refreshed.

Meanwhile, members of Anatoly Scharansky's family said that the Supreme Soviet has issued a special decree authorizing up to six more months of detention without trial for the Jewish dissident, who reportedly is being investigated on a charge of treason. He was arrested nine month ago.