Sen. John P. East (R-N.C.), hospitalized April 20 for acute hypothyroidism, remains in "satisfactory condition" and is expected to be released "within the next three weeks."

In a statement released by East's office, Dr. John O'Brian, chairman of endocrinology at Bethesda Naval Hospital, said East was "responding quite well to treatment and a complete recovery is anticipated."

The statement followed inquiries from The Washington Post as to whether the senator's condition might be more serious than first reported.

East, 54, was admitted to the hospital after complaining of insomnia and fatigue. His condition, described as a "chemical imbalance which can be medically corrected," is produced by defective activity of the thyroid gland, which controls metabolism.

Yesterday's statement said East's doctors are still trying to determine the right dosage of medication.

"The treatment consists of gradually restoring the body's normal thyroid hormone levels through the use of synthetic hormones," the statement said. "East's release from the hospital depends upon achieving the proper hormone levels, which Dr. O'Brian said he expects to occur within the next three weeks."

Little is known of the causes of thyroid deficiency, according to Black's Medical Dictionary, but "the great majority of cases arise in middle life, between the ages of 30 and 50."

East, elected to the Senate in 1980, was hospitalized in February for removal of a benign obstruction of the urinary tract.