WASHINGTON (AP) _ Soviet dissident Andrei Sakharov is presumed to have resigned from the prestigious Soviet Academy of Science in protest over the refusal of Soviet authorities to let his wife seek medical care abroad, a spokesman for the Andrei Sakharov Institute here said Friday.

Edward Lozansky, the institute director, said the group received a report from a ''vry reliable source'' three weeks ago that Sakharov would resign if action wasn't taken by May 10 to let his wife, Yelena Bonner, leave.

Lozansky said Mrs. Bonner apparently is in need of a heart bypass operation.

Since nothing was done, Lozansky said there is no doubt that Sakharov has resigned. ''He is a man of his word.'' But he said it could not be confirmed.

The State Department said also it could not confirm the resignation.

Lozansky said Sakharov's resignation would be the first from Soviet Academy of Science, which existed long before communist rule, in its 260-year history. ''It puts disgrace and shame on the whole country,'' he said.

Sakharov, a nuclear physicist and winner of the 1975 Nobel Peace Prize, was banished from Moscow to the closed city of Gorky in 1980 because of his outspoken views. His wife was sentenced to five years of internal exile in Gorky last summer for slandering the state.

Gorky is 250 miles east of Moscow and closed to foreigners.